Tool List- www.amazon.com/shop/acservicetech Support- www.patreon.com/acservicetech For those that are looking for the tools used in the videos: (Linked Below) Here is the Link for the Yellow Jacket Refrigerant Manifold Gauge Set used in the videos- amzn.to/2aenwTq Here is a link to Refrigerant hoses with valves used in the videos- amzn.to/2aBumVI Here is a link to the UEI DL389 Multimeter used in the videos- amzn.to/2xAdaJf Here is a link to the Imperial 535-C Kwik Charge Vaporizer for Charging Refrigerant- amzn.to/2wFHtBW Here is the link to the Fieldpiece ST4 Dual Temp Meter- amzn.to/2wc1ME3 Here is a link to the Digital Refrigerant Scale used in the videos- amzn.to/2b9oXYl Here is a link for RectorSeal Bubble Gas Leak Detector amzn.to/2ckWACn Other tool links can be found in the video description section. ACSERVICETECH is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon. Check out other videos on the HVACR topics of interest at- ruclips.net/channel/UCOZR-1IqsAer9wzlvFgb4mAplaylists?view_as=public If you want to support the ACSERVICETECH Channel and receive more HVAC content, check out www.Patreon.com/acservicetech
Thank you! I had new AC units installed May of 2022. In September one of the units stop blowing cold. It is under warranty, the tech came out & identified the TXV was bad, he then said they would replace it with a piston that is more reliable. I have a friend that has been in the business for 30yrs, something prompted me to run it by him to see if the tech was correct. He said no, get them to replace the TXV because of the efficiency. I called the company to let them know, & expressed my dissatisfaction with a lesser technology being installed in the system than what I paid for. The owner called me back & said my friend was incorrect, but they will install a TXV if I wanted. My friend also said they should replace the dryer since it was probably junk in the line or possibly the bulb was damaged because a TXV shouldn't fail so soon. I stuck with my friends advice, then saw this video & it validated him.
You need to ask you freind how much it cost to replace your txv...if its out of warranty...do all the evacuation...refrigerant recovery.....etc...i bet you if cost more than cost saving of the tvx...i work on air cond for over 30 years...never had a piston to fail.....but tons of expansion valves....i even changed the one in my own home from a txv to piston....realibity more important than effiency....imho...
Awesome thanks Andrew and make sure to check out an article I just posted on the TXV bulb location vs external equalize location at www.acservicetech.com/articles
Wow, I've worked in the HVAC field for 45 years (that's correct, I'm an old man😉) and instructed many beginners over the years, but I've never been able to explain the operation of a TXV as well as you did! GREAT JOB!!!
The best and most visually descriptive explanation about the differences between TXVs and piston metering valves that I have found. Really great video!
Love your videos, helping me big time. Been an installer for about 2.5 years, and im wanting to learn how the full system works instead of just knowing "that goes there and it just works". You have lots of detail. Thank you for posting these videos👍
This is an A++ Video on a txv vs. Piston application. Had a customer ask what the difference was and why. Good explanation. Thank you for the videos. HVAC ON!!!
Good video. Advantages to the homeowner is always a good thing to know. Superior humidity control because of better moisture removal (especially on cooler days) and easier and more accurate charging for lower cost operation are good talking points.
Always very informative. I do find it harder to get my pressures on point when it's and older system with a piston. Nothing better than a nice TXV that reacts immediately when you add a few ounces. I find that the piston's don't always react well on my suction pressure and will just raise my head pressure then I switch over to my testos and put my temp clamps on and check my superheat so I don't over charge but I find it much easier to check my sub cooling,
Yesterday I installed ICP N coil 3 tons with TXV(I don't like them at all. I always go with piston setup but dimensions were limited so end up using this type of coil) turn it on and I was reading 135 psi -3SH on my suction, 250 psi 6 SC. Outside 75, house wet bulb was 72. I was so mad at the txv being open because it was flooding but after this video I hope to see it 5SH or more when I go there to check it next week, under normal conditions in the house. Great video thanks for sharing.
Well, the txv should always hold a factory set or tech set superheat. Some txv's are non adjustable. The txv allows more refrigerant through when the load is high but will still maintain the same superheat. On a day that has lees of a load, the txv will let less refrigerant into the coil but will maintain the same 10-14 degree superheat. If you have 0 or negative superheat, something is very wrong. Check to make sure the txv is 3 tons if the outdoor unit is 3 tons. Make sure the bulb to snug to the suction tube. You could try to adjust the txv if it is an adjustable model. Or you could also try putting the bulb in hot water then cold water then hot water again to get the inside moving, verify it is moving. It could be stuck wide open. Also you could try moving the bulb outside of the coil box on the suction line. Anyway, there are some ideas but don't let it run with 0 superheat or less because that would hurt the compressor if it is a single or two speed compressor that is on a conventional system and doesn't have an accumulator to protect the compressor, thanks
acservicetech I m going back there to check it again. I was also suspicious about my Testo gauge set. I ll check it again and try the hot and cold water trick to make it moving. Thanks a lot.
Well DIY the new system in my house and the outdoor unit came with a piston . So I went back inside and took the inside oil box apart I saw that had a TXV this video helped me knowing that I have either one or the other but not both thank you
Outdoor unit is a compressor, compress vapor, and condensetes to liquid for the Txv,or piston, to reduce temperature, allowing refrigerant to absorb heat
I just wanted to point out, I did snap this bulb back on with the clip with the stub on the top. The stub should always be on the lower side and the tube going to the txv should be higher so it is just vapor going to the head of the txv. I just wanted to point that out before anyone asked and didn't want anyone confused by that. My apologies, it was late here when I did this and was just trying to get the video out. Thanks!
Very well executed! I have a question, I was always taught that the txv bulb should be insulated to sense line temperature rather than having it exposed and sensing air inside the cabinet potentially leading to an overcharged system if not careful. Thanks for sharing your wisdom!
Some manufacturers insulate the txv in the cabinet and some don't. When I install them I insulate them to be safe and also the tube from the bulb that carries the refrigerant to the txv should be up and the stub should be lower when horizontal. I realized that I did that after I made the video, ha. Thanks
Thorough, well presented, explanation of how this device works. I wish some long-time HVAC techs would review (and understand) the principles and operation of TXVs. 99% of the valves I've replaced died because they were plugged with crud, not because the valve failed in any way. Regardless, if the problem was the "Copeland" compressor rust inhibitor issue or a bad initial install (no nitrogen purge), the "actual" problem normally is "not" the TXV.
Thank you for sharing your insight and years of experience which is true teaching through experience or truly evolved special knowledge which is priceless great job.
Txv is Cadillac of metering devices. Maintains desired superheat. Makes troubleshooting easier. But very sensitive and harder to replace than a piston. After piston fails on new instal I recommend txv as replacement.
in my experience i much rather have the fix piston versus the expansion valve...you have to change it out at aprox 10 years at least....and what little you save....is lost big time.......and it sensitive like when copeland oil additive issues back a few years ago....realiblity is more important than effeciency...in my opinion....great video...
I wished that my family's evap coil had a TXV vs a piston. First, some info on the system. It is a York system. Air handler I believe is a 4 ton and the condensing unit is 3.5 ton. It has a 3.5 ton sized piston in the evap coil. It cools alright but all it can muster is a 13 degree delta T. The system has a LOT of airflow and blows pretty good. As far as I know, the system has the correct refrigerant charge. Condensing unit is a microchannel (gasp!!) and has a charging / temp chart on the unit (can't go by superheat). I'm sure that the delta T would improve if it ran longer (probably maxing out at 15-16). The set point is 75 on the thermostat. While TXV's can go bad, it's my belief that the delta T would be slightly improved if the evap coil had a TXV.
Oh man, i love ur Chanel, Now i understant perfectly and can see what happening in the condenseur and evap. my first language Is french and m'y english Is not vert good but ur explaination Is very clear and its more easy to me to understant. Big big thnx. Im better than ever Now ;) i just need a psychrometer to find the correct super heat ween i have à piston at job 😄💪👌👍👍👍
I have the "General digital psychrometer" linked at amazon.com/shop/acservicetech - I think it was like $77 but I used that one for years. There is also the Fieldpiece one that links to the SMAN 460, thanks
I've got about 20 rental properties in south Texas were it's in the mid 90s about 6 months of the year. I have fixed orfice (piston) metering on all my units and I don't care what any tech says I'll never use TXV. Txv get stuck, and cause more problems that they are worth. Txv also are hard on compressiors because the pressures don't fully equalize on high/low side like a fixed orfice. I don't care if fixed orfice is slightly less efficient the headache of txv just isn't worth a slight efficiency gain.
If you pause video at 2:01 you see two types of pistons. You said "older style piston" is bottom and "newer type" is top. My research indicates that the bottom piston is a Carrier type and the top is a Goodman type. Questions: is that true? ; can you interchange the "old type" with the "new type" ? ; in other words, if the pistons are brand specific can they be interchanged?
you mention about fan motor stoping and with a piston...and floods....more time than not i seen expansion valves lock up....and cause compressor to lock out....i even seen a expansion valve lock up during defrost cycle on a Heil unit before...
Thank you for this video as a homeowner. Our 16 yr Amana Prestige 2 quit working after being gone for 10 days with high temps outside...I had left the thermostat at 80 deg. When we got back, apparently the Evaporator froze up. The initial HVAC repair person told us we needed either a new Central Air System for $4K or he could replace the Coil for $1700. I replaced the TXV and the system is working perfectly. My question is, what caused the TXV to fail...and exactly how did it fail? Did it get stuck closed...which caused low refrigerant...thus freezing the coil? In the future, would I have been better off, slowly adjusting the thermostat down like from 80 to 76, 76 to 73, etc...would that prevented damage to the TXV? Thank you!
You should be able to set the tstat at any temp 68 or above in cooling and be able to run until it gets down to there with no problem. The txv could be bad due to manufacturer defect, brazing too close to it, brazing without nitrogen, anti corrosion compound in the compressor oil from the factory, bulb tube bent and leaked refrigerant from the bulb. Make sure you are epa 608 certified before handling refrigerants, thanks Todd!
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Are the screw caps on the orifice/piston and TXV compatible on the distributor side? If not, what normally technicians do when a piston is replaced with a TXV? Completely remove the distributor small pipes? Can you do a video for that. I completely self study and would like to know what’s the normal procedure to do the convention. I searched on RUclips and didn’t find any good videos to describe all the concerns about the replacement. You always give best great videos. Thank you for your efforts
Glad to help and you will keep the same distributor tubes that are there regardless of the metering device type. The distributors are sized for the coil and the average flow of the piston and txv should be similar. It is just that the txv will be more efficient when there is a higher heat load at the evap coil, thanks!
I have a piston unit, where should I measure the superheat, at the evaporator outlet line or outdoors at the condensing unit suction line? The condensing unit label says "indoor TXV Subcooling 13deg but was installed with a fixed orifice, so what should the superheat be and aging what location to measure the suction lime temp? I was under the impression the entire evaporator should draw sweat including up to the outlet manifold.
My newly installed GMan 3.5 ton HP is sweating on outside of evap cabinet and lot of water under outside condenser. Tech replaced TXV with piston in hope of fixing, Is this right??
I had a new evap coil installed and they forgot to install the orifice piston and the system was running for 2 months without the orifice installed. Can the compressor be damaged with this missing? Also when they discovered that the piston was missing they opened the line installed the piston and did not vacuum the system down and just added refrigerant.
Hi mate I have a question according to the information below Unit is ducted split system r22 Suction line actual temp was 24 to 25 Celsius Suction line saturated temperature on guage was below 0 around minus 8 or 9 degree when the unit was on cooling mode( I have regassed it according to reading plate and fixed the leak of Schrader valve as well before any action) Discharge line pressure 240 250 psig Metering device was not mentioned on reading plate but I checked the indoor unit it was piston device or capillary (definetly not txv) so the super heat too high And discharge temperature 32 33 Celsius ( too much pressure was stored behind metering device in my opinion) Condense dry bulb 26 27 Celsius I'm in Australia My question is that Can we make sure that there is blockage in metering device of indoor unit? If or could this blockage be somewhere else which I don't think so. What's your technical opinion. Do I have to replace the metering device only or some more parts? Many thanks I do appreciate
It sounds like there is a restriction like you were mentioning since there is such a low suction pressure and high sat temp. If the outdoor unit is just a outdoor condensor and not heat pump then I would suggest replacing the filter drier, piston, and strainer screen right before the strainer. On a heat pump, the inactive metering device may be before or after the liquid line port. If the evap has cap tube installed, I would replace the evap with one capable of having a piston or txv. I will always install a txv though, thanks
thanks for the great video. i always thought that high outdoor temp on hot days will pushed more refrigerant through orifice (more pushing pressure) than on cooler days. BUT, you're saying the SAME AMOUNT of refrigerant goes into the evaporator ALL the times. Please help to clarify. thank you.
Thank you Craige for informative video. Q:I got a ductless mini split 24 BTU utilizes with piston not EEV is possible to check the refrigerant like central air conditioning? Thanks.
Just curious....could you attach a thermistor sensor inside the coil in series with the condenser low voltage to shut the system down on low ambient days?....Great videos...I look for to getting them
You could. That is the concept with economizers so that instead of turning on the compressor, it pulls fresh air in from outside instead. Thanks Michael Madrigal!
@@acservicetechchannel you are very welcome another thing to add on to what I said is that you work very clean and you are very well spoken you are very articulate explaining things but you do not use language that is over complicated which I love about your Channel God bless you and your beautiful family I wish you continued success I will be going to HVAC school January 12th God willing I am missing my right hand but I was born that way and I am also a licensed Barber and a licensed real estate agent in Florida figured I pick up another trade and I always find a way to do the work I also saw how you did the flare on the pipe which is so clean it was so impressive but I noticed that there is a gun that does that for you or a drill I guess you would call it, expensive but I think it would benefit me a whole lot either way sorry for the long winded message encouragement to you my brother keep on being the pro that you are
David, I really appreciate your note and may the Lord Bless you as well! I am glad you are encouraged by the videos and Florida is probably a very nice location for an HVACR tech, thanks again!
Most brands will take the ones I showed in the video but there are also smaller versions as well with piston chambers that loosen clockwise instead of counterclockwise. Thanks Channel Cat Chaser!
I disagree with the statement that a txv works better instantly. I usually need to let it run 1-2 hours so that the sensing bulbs eventually loses pressure after being strapped to the suction line before the equalizer and then is open and floods that evap better. I’ve over charged several systems going off subcool IMMEDIATELY after start up. Maybe just a Texas thing since the txv was sitting in a 120f truck and the bulb was pressurized and shut tight
After 10 minutes, you can check the charge with subcooling but still monitor the superheat for diagnosis. The refrigerant is in the system and you can see the levels by reading both superheat and subcooling. As the system runs, the txv lets less refrigerant into the evap since the heat load is lowering. When a bulb is at 120 the orifice inside the txv is more open instead of shut since there is so much opening pressure but yes overall the longer you run a system, the more accurate you will be, thanks!
Do people use Humidifiers in the winter time there? Id like to see a video on Humidifiers. I recently came across a Humidifier installed with an ecobee3 thermostat and both sets of wiring configurations left a new humidifer to not work or work intermittently.
hi, if i were to replace a piston with a txv. how would i size it? does new txv comes with a pre-set superheat already? i saw a new txv from supplier bag and it says 18-36BTU. thank you.
How does an overcharged system with TXV effect Superheat/Subcooling and compressor cycling? Does the TXV maintain the same superheat and evap pressure with varying liquid pressure at the TXV?
The txv will try to maintain the same superheat even if the subcooling is high. The compressor amps will be higher and the heat rejection capability will be less at the outdoor unit if it is overcharged, thanks!
Love the videos! I have a few questions. Do you install or service and Goodman, Amana or Daikin equipment? I’ve been trying to get a few answers but can’t seem to get them. I always install TX Valves on my new systems and I always stick with Amana because they have scroll compressors. The Goodman units comes with a rotary which calls for a hard start kit if you were to install a TX Valve on that condenser. My question is, the 13 SEER unit calls for a TX valve by Emerson which is adjustable. The 16 SEER and higher units call for a TX Valve by danfoss which is not adjustable. What is the purpose of having a TX Valve that is adjustable? I understand that you need to charge the system based on sub-cooling, but do you need to take your drybulb and wet bulb readings with a TX valve that is adjustable and adjust the valve to that superheat? I wouldn’t say from the factory that they Valve is set to a point where you don’t need to adjust it? Also when you are checking a system with a TX Valve and you check your subcooling, is your superheat going to be relatively close to the same as your target subcooling? Do you check drybulb, wet bulb to find target superheat and adjust if necessary? Or do you charge only subcooling and call it a day?
So most AC unit TXV systems are nonadjustable. In the case of a TXV that is adjustable, they are usually set close to the normal superheat needed. You would normally run the ac unit and set the subcooling to the correct amount. Then you would check to see if the txv is working properly around 8 to 16 degrees of total superheat. Normally they operate around 10-14 degrees but for a new system install, they may take some time to settle into the correct superheat, thanks!
Gerry Cui really I hope this isnt a real question....if you think u need to drill a hole an use a camera to see if they are using a piston or Txv for a metering device you shouldn't attempt anything
Another great lesson! What does the other capillary tube go to from the TXV on the upper left, Craig? It looks like everything with TXV is threaded, not brazed, right? Thanks for posting!
The tubing coming off of the txv bulb head is connected to the txv bulb and the other tube is connected to an external equalization port to check pressure at that location. Where the external equalization port attaches to the suction line there is a 1/4" flare. Most manufacturers now braze that line into the suction line. The txv seals on both sides with teflon rings. Thanks
Connections at TXV depend on manufacturer, some are flare others are brazed in. As to the capillary tube on left upper side I have seen coils with sensing bulbs on the coil itself, but it is hard to tell where and how it lands from video. Note that the TXV only uses one sensing bulb to meter superheating though and it it most likely the equaling line.
Just a really good RUclips channel to either brush up on or learn forced air from. Probably the best guy here I have seen, not the only one taking the time to teach for free, but with the amount of professional incompetence I have seen posted as 'Pro's", this guys is top tier. Thanks ACSERVICETECH for taking the time to teach !
Yes recover or pump down, then when the system is at 0psig, replace with the txv, followed by a pressure test, and then vacuum, before breaking the vacuum with refrigerant, thanks
I was at initial startup inside space was 85 degrees 150psi/390psi 410a super heat was 4 degrees and subcool was at 13 degrees, 22 degree delta t . Why is txv not keeping the 10-15 degree super heat ? 4 degrees is kinda low wouldn’t it ? Please advise thanks for your videos
Seems like the txv is stuck in the open position or the txv is too big compared to the system. Is the evap coil small compared to txv and condensor or is the txv size bigger than the evap or evap and condensor? Also, if it is an initial startup, did the person who brazed it keep the bulb on the suction line while brazing next to it? That would have exerted a lot of pressure down on the txv as opening force. If everything looks ok size wise, I would try cycling the txv back and forth before and while it is running with hot tap water and ice water and switching the bulb back and forth between the cups of water. Maybe leave them in for 20-30 seconds each. You don't want to leave it in the hot water too long as you will not have any superheat for the compressor which would mean sat state refrigerant can get into the compressor. Anyway, those are some thoughts. I hope it helped!
When brazing your line sets and purging the system with nitrogen are there any issues with the nitrogen flowing through the txv, as long as the temp sensing bulb is at a temperature that the valve would see as demand it should be wide open right ?
Can I use bigger TXV to replace smaller Piston? For example, 5 ton TXV to replace piston on a 2 ton unit? Since the TXV can adjust the refrigerant flow, so it should be able to handle it. Is that right? Thank you so much for your nice videos!
@@acservicetechchannel Thank you for your quick response. One more question, are the screw caps compatible on piston and txv? If not, I have replace the cut off small tubing on the other side of distributor? Thank you again
That sounds like your indoor airflow is not high enough or there is some blockage since you are absorbing heat outside but not able to reject it inside, thanks
Does it matter if a txv mounts inside or outside the coil cabinet? I have a New Goodman with an A coil and removing piston and adding txv before install.
It does not matter but if it is outside, the txv must be insulated because it will have low temp refrigerant running through it so it would allow condensation of any humidity, thanks!
AC Service Tech LLC Good deal and thank you for getting back to me. It’s a Goodman TX3N4 and comes with a round insulation cup that fits the txv and velcro’s shut.
Yes the txv typically is not able to shut down completely but it lets a lot less refrigerant into the evap than the piston. That is much better for the compressor in terms of how much saturated refrigerant is entering into it, thanks a lot Kevin
I only replace piston with a txv for efficiency and compressor safety. I think some people take out txv's and replace them with a piston because they don't understand how txv's work maybe. They are pretty reliable and worth keeping, thanks
Hi! How do I recalculate/recompensate for the lost oil xoes goes with the refrigerant on recovery? Is there any mathematical formula to determine jow mu h oil is left on the system parts after the recovery?
Actually it is very hard to determine that unless you have an oil separator in the line like car type recovery units. This is since you can't identify if it is oil or liquid refrigerant weight in the bottom of the recovery tank. There is much more oil in a split system or packaged unit than in a car. For the most part on a standard system that has not been recovered more than once the oil level should be adequate after recovery still.
acservicetech, thanks for responding. Right now, Im working on my car and I lost my refrigeration through a leaking core. I forgot to put back the cap after used the gauges (where I found both pressures are loe) and my A/C wont run in the morning. Any advice.
Excellent video. What do you recommend to seal the threads on a fixed orifice and TXV? Ive seen cases where a system is low on refrigerant and the nut is tight but the leak is from the threads. Do you recommend leak-lok on these?
Typically the leaks are not coming from the threads but the seal face. A teflon ring is used near txvs or a flare with refrigerant oil or something like nylog is used but only on the face of the seal. Thanks!
Kind of like a carbeurator vs fuel injected. The Car computer keeps the air/fuel mixture perfect no matter what temp and it works great until it fails. Seems a TXV does a similar job as it keeps the amount of refrigerant that passes through at a perfect level based on temperature.
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Tool List- www.amazon.com/shop/acservicetech
Support- www.patreon.com/acservicetech
For those that are looking for the tools used in the videos: (Linked Below)
Here is the Link for the Yellow Jacket Refrigerant Manifold Gauge Set used in the videos- amzn.to/2aenwTq
Here is a link to Refrigerant hoses with valves used in the videos- amzn.to/2aBumVI
Here is a link to the UEI DL389 Multimeter used in the videos- amzn.to/2xAdaJf
Here is a link to the Imperial 535-C Kwik Charge Vaporizer for Charging Refrigerant- amzn.to/2wFHtBW
Here is the link to the Fieldpiece ST4 Dual Temp Meter- amzn.to/2wc1ME3
Here is a link to the Digital Refrigerant Scale used in the videos- amzn.to/2b9oXYl
Here is a link for RectorSeal Bubble Gas Leak Detector amzn.to/2ckWACn
Other tool links can be found in the video description section.
ACSERVICETECH is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.
Check out other videos on the HVACR topics of interest at- ruclips.net/channel/UCOZR-1IqsAer9wzlvFgb4mAplaylists?view_as=public
If you want to support the ACSERVICETECH Channel and receive more HVAC content, check out www.Patreon.com/acservicetech
acservicetech looking for information on heat pumps
Tony check out the Heat Pump playlists on the channel page!
Thanks for the awesome videos man. I was just wondering if you could please explain how the equalization tube works.
Thank you! I had new AC units installed May of 2022. In September one of the units stop blowing cold. It is under warranty, the tech came out & identified the TXV was bad, he then said they would replace it with a piston that is more reliable. I have a friend that has been in the business for 30yrs, something prompted me to run it by him to see if the tech was correct. He said no, get them to replace the TXV because of the efficiency. I called the company to let them know, & expressed my dissatisfaction with a lesser technology being installed in the system than what I paid for. The owner called me back & said my friend was incorrect, but they will install a TXV if I wanted. My friend also said they should replace the dryer since it was probably junk in the line or possibly the bulb was damaged because a TXV shouldn't fail so soon. I stuck with my friends advice, then saw this video & it validated him.
You need to ask you freind how much it cost to replace your txv...if its out of warranty...do all the evacuation...refrigerant recovery.....etc...i bet you if cost more than cost saving of the tvx...i work on air cond for over 30 years...never had a piston to fail.....but tons of expansion valves....i even changed the one in my own home from a txv to piston....realibity more important than effiency....imho...
Thank you for explaining. Could not find anyone else who explained this clearly without being totally confusing.
Awesome thanks Andrew and make sure to check out an article I just posted on the TXV bulb location vs external equalize location at www.acservicetech.com/articles
Wow, I've worked in the HVAC field for 45 years (that's correct, I'm an old man😉) and instructed many beginners over the years, but I've never been able to explain the operation of a TXV as well as you did! GREAT JOB!!!
The best and most visually descriptive explanation about the differences between TXVs and piston metering valves that I have found. Really great video!
Glad you liked it!
Love your videos, helping me big time. Been an installer for about 2.5 years, and im wanting to learn how the full system works instead of just knowing "that goes there and it just works". You have lots of detail. Thank you for posting these videos👍
Thank you very much Deon, glad to help!
Mr. you got to be one of the best..... out there explaining hvac systems and how they work, thanks
Thanks a lot Ali Baba!
Awesome teacher. God bless you. Thank you for your time. I'm hvac student and learned so much from you. Appreciate it.
This is an A++ Video on a txv vs. Piston application. Had a customer ask what the difference was and why. Good explanation. Thank you for the videos. HVAC ON!!!
Thanks Ray Ray!
Good video. Advantages to the homeowner is always a good thing to know. Superior humidity control because of better moisture removal (especially on cooler days) and easier and more accurate charging for lower cost operation are good talking points.
Absolutely, awesome insights!
Always very informative. I do find it harder to get my pressures on point when it's and older system with a piston. Nothing better than a nice TXV that reacts immediately when you add a few ounces. I find that the piston's don't always react well on my suction pressure and will just raise my head pressure then I switch over to my testos and put my temp clamps on and check my superheat so I don't over charge but I find it much easier to check my sub cooling,
Yesterday I installed ICP N coil 3 tons with TXV(I don't like them at all. I always go with piston setup but dimensions were limited so end up using this type of coil) turn it on and I was reading 135 psi -3SH on my suction, 250 psi 6 SC. Outside 75, house wet bulb was 72. I was so mad at the txv being open because it was flooding but after this video I hope to see it 5SH or more when I go there to check it next week, under normal conditions in the house. Great video thanks for sharing.
Well, the txv should always hold a factory set or tech set superheat. Some txv's are non adjustable. The txv allows more refrigerant through when the load is high but will still maintain the same superheat. On a day that has lees of a load, the txv will let less refrigerant into the coil but will maintain the same 10-14 degree superheat. If you have 0 or negative superheat, something is very wrong. Check to make sure the txv is 3 tons if the outdoor unit is 3 tons. Make sure the bulb to snug to the suction tube. You could try to adjust the txv if it is an adjustable model. Or you could also try putting the bulb in hot water then cold water then hot water again to get the inside moving, verify it is moving. It could be stuck wide open. Also you could try moving the bulb outside of the coil box on the suction line. Anyway, there are some ideas but don't let it run with 0 superheat or less because that would hurt the compressor if it is a single or two speed compressor that is on a conventional system and doesn't have an accumulator to protect the compressor, thanks
acservicetech I m going back there to check it again. I was also suspicious about my Testo gauge set. I ll check it again and try the hot and cold water trick to make it moving. Thanks a lot.
Well DIY the new system in my house and the outdoor unit came with a piston . So I went back inside and took the inside oil box apart I saw that had a TXV this video helped me knowing that I have either one or the other but not both thank you
Outdoor unit is a compressor, compress vapor, and condensetes to liquid for the Txv,or piston, to reduce temperature, allowing refrigerant to absorb heat
Awesome explanation on the difference between a txv and a piston.
I just wanted to point out, I did snap this bulb back on with the clip with the stub on the top. The stub should always be on the lower side and the tube going to the txv should be higher so it is just vapor going to the head of the txv. I just wanted to point that out before anyone asked and didn't want anyone confused by that. My apologies, it was late here when I did this and was just trying to get the video out. Thanks!
Very well executed! I have a question, I was always taught that the txv bulb should be insulated to sense line temperature rather than having it exposed and sensing air inside the cabinet potentially leading to an overcharged system if not careful. Thanks for sharing your wisdom!
Some manufacturers insulate the txv in the cabinet and some don't. When I install them I insulate them to be safe and also the tube from the bulb that carries the refrigerant to the txv should be up and the stub should be lower when horizontal. I realized that I did that after I made the video, ha. Thanks
The best teacher l learned so much from this guy
Thorough, well presented, explanation of how this device works. I wish some long-time HVAC techs would review (and understand) the principles and operation of TXVs. 99% of the valves I've replaced died because they were plugged with crud, not because the valve failed in any way. Regardless, if the problem was the "Copeland" compressor rust inhibitor issue or a bad initial install (no nitrogen purge), the "actual" problem normally is "not" the TXV.
You are absolutely correct and thank you very much for your great comments!
Thank you for sharing your insight and years of experience which is true teaching through experience or truly evolved special knowledge which is priceless great job.
So well explained! Thank you!
Thanks Meteora!
Txv is Cadillac of metering devices. Maintains desired superheat. Makes troubleshooting easier. But very sensitive and harder to replace than a piston. After piston fails on new instal I recommend txv as replacement.
Never had a piston fail but had seen many txvs fail and take out compressors :(
in my experience i much rather have the fix piston versus the expansion valve...you have to change it out at aprox 10 years at least....and what little you save....is lost big time.......and it sensitive like when copeland oil additive issues back a few years ago....realiblity is more important than effeciency...in my opinion....great video...
Good guy, you are gifted for teaching 👍
I appreciate that!
The txv are so awesome.
Excellent explanation of the processes. Thank You!
Thanks Bill!
I wished that my family's evap coil had a TXV vs a piston. First, some info on the system. It is a York system. Air handler I believe is a 4 ton and the condensing unit is 3.5 ton. It has a 3.5 ton sized piston in the evap coil. It cools alright but all it can muster is a 13 degree delta T. The system has a LOT of airflow and blows pretty good. As far as I know, the system has the correct refrigerant charge. Condensing unit is a microchannel (gasp!!) and has a charging / temp chart on the unit (can't go by superheat).
I'm sure that the delta T would improve if it ran longer (probably maxing out at 15-16). The set point is 75 on the thermostat.
While TXV's can go bad, it's my belief that the delta T would be slightly improved if the evap coil had a TXV.
You should be able to get 18-21 delta T with a txv and a proper charge, thanks Ronnie
Oh man, i love ur Chanel, Now i understant perfectly and can see what happening in the condenseur and evap.
my first language Is french and m'y english Is not vert good but ur explaination Is very clear and its more easy to me to understant. Big big thnx.
Im better than ever Now ;) i just need a psychrometer to find the correct super heat ween i have à piston at job
😄💪👌👍👍👍
I have the "General digital psychrometer" linked at amazon.com/shop/acservicetech - I think it was like $77 but I used that one for years. There is also the Fieldpiece one that links to the SMAN 460, thanks
acservicetech i Buying sman460 last week and i think i Will Buy the spychometer for this. Thnx teacher for ur heap and Tuto.
Glad to help, thanks
I've got about 20 rental properties in south Texas were it's in the mid 90s about 6 months of the year. I have fixed orfice (piston) metering on all my units and I don't care what any tech says I'll never use TXV. Txv get stuck, and cause more problems that they are worth. Txv also are hard on compressiors because the pressures don't fully equalize on high/low side like a fixed orfice. I don't care if fixed orfice is slightly less efficient the headache of txv just isn't worth a slight efficiency gain.
If you pause video at 2:01 you see two types of pistons. You said "older style piston" is bottom and "newer type" is top. My research indicates that the bottom piston is a Carrier type and the top is a Goodman type. Questions: is that true? ; can you interchange the "old type" with the "new type" ? ; in other words, if the pistons are brand specific can they be interchanged?
Man, I love your videos, very well explained. Thanks
Thanks a lot Joe!
Great technical information and really well explained. Thank you!!!
Thank you polymyxa!
you mention about fan motor stoping and with a piston...and floods....more time than not i seen expansion valves lock up....and cause compressor to lock out....i even seen a expansion valve lock up during defrost cycle on a Heil unit before...
Excellent video.
I would like to see a video on custom evaporator case fabrication. Thank you
Thanks for letting me know Ron!
Damn, amazing video I learned alot thank you.
Thank you for this video as a homeowner. Our 16 yr Amana Prestige 2 quit working after being gone for 10 days with high temps outside...I had left the thermostat at 80 deg. When we got back, apparently the Evaporator froze up. The initial HVAC repair person told us we needed either a new Central Air System for $4K or he could replace the Coil for $1700. I replaced the TXV and the system is working perfectly. My question is, what caused the TXV to fail...and exactly how did it fail? Did it get stuck closed...which caused low refrigerant...thus freezing the coil? In the future, would I have been better off, slowly adjusting the thermostat down like from 80 to 76, 76 to 73, etc...would that prevented damage to the TXV? Thank you!
You should be able to set the tstat at any temp 68 or above in cooling and be able to run until it gets down to there with no problem. The txv could be bad due to manufacturer defect, brazing too close to it, brazing without nitrogen, anti corrosion compound in the compressor oil from the factory, bulb tube bent and leaked refrigerant from the bulb. Make sure you are epa 608 certified before handling refrigerants, thanks Todd!
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Are the screw caps on the orifice/piston and TXV compatible on the distributor side? If not, what normally technicians do when a piston is replaced with a TXV? Completely remove the distributor small pipes? Can you do a video for that. I completely self study and would like to know what’s the normal procedure to do the convention. I searched on RUclips and didn’t find any good videos to describe all the concerns about the replacement. You always give best great videos. Thank you for your efforts
Glad to help and you will keep the same distributor tubes that are there regardless of the metering device type. The distributors are sized for the coil and the average flow of the piston and txv should be similar. It is just that the txv will be more efficient when there is a higher heat load at the evap coil, thanks!
The expansion valve should have maximum opening, then just put a piston the same size of the opening. Expansion valves break a lot.
What about Piston ? Do they fail alot?
Thanks !
I have a piston unit, where should I measure the superheat, at the evaporator outlet line or outdoors at the condensing unit suction line? The condensing unit label says "indoor TXV Subcooling 13deg but was installed with a fixed orifice, so what should the superheat be and aging what location to measure the suction lime temp? I was under the impression the entire evaporator should draw sweat including up to the outlet manifold.
I understand that TXVs are more efficient, but which device (TXV vs Piston) is most reliable for comfort cooling in a place like Florida.
Fantastic Ty
Excellent.... so many thanks :)
I bought a new a-coil that took a TXV and the opening of the distribution tubes had a schrader valve, why was the valve there?
Great help and very well explained.
Thanks a lot s man and if you have any technical questions feel free to email me at info@acservicetech.com! Thank you for your support on Patreon!
Formula to find super heat
Wet bulb x 3 - 80 - outdoor temp divided by 2 = TSH
Great video!!! Like always , Thank you ..
My newly installed GMan 3.5 ton HP is sweating on outside of evap cabinet and lot of water under outside condenser. Tech replaced TXV with piston in hope of fixing, Is this right??
I had a new evap coil installed and they forgot to install the orifice piston and the system was running for 2 months without the orifice installed. Can the compressor be damaged with this missing? Also when they discovered that the piston was missing they opened the line installed the piston and did not vacuum the system down and just added refrigerant.
Great job and video like always
What would happen if the outdoor unit says TXV metering is needed and a piston is installed instead?
Are the two piston types "old" vs "new" interchangeable? Or are they brand specific?
Hi mate I have a question according to the information below
Unit is ducted split system r22
Suction line actual temp was 24 to 25 Celsius
Suction line saturated temperature on guage was below 0 around minus 8 or 9 degree when the unit was on cooling mode( I have regassed it according to reading plate and fixed the leak of Schrader valve as well before any action)
Discharge line pressure 240 250 psig
Metering device was not mentioned on reading plate but I checked the indoor unit it was piston device or capillary (definetly not txv) so the super heat too high
And discharge temperature 32 33 Celsius ( too much pressure was stored behind metering device in my opinion)
Condense dry bulb 26 27 Celsius
I'm in Australia
My question is that
Can we make sure that there is blockage in metering device of indoor unit? If or could this blockage be somewhere else which I don't think so. What's your technical opinion. Do I have to replace the metering device only or some more parts?
Many thanks
I do appreciate
It sounds like there is a restriction like you were mentioning since there is such a low suction pressure and high sat temp. If the outdoor unit is just a outdoor condensor and not heat pump then I would suggest replacing the filter drier, piston, and strainer screen right before the strainer. On a heat pump, the inactive metering device may be before or after the liquid line port. If the evap has cap tube installed, I would replace the evap with one capable of having a piston or txv. I will always install a txv though, thanks
thanks for the great video. i always thought that high outdoor temp on hot days will pushed more refrigerant through orifice (more pushing pressure) than on cooler days. BUT, you're saying the SAME AMOUNT of refrigerant goes into the evaporator ALL the times. Please help to clarify. thank you.
it is the same amount at all times with piston.
Thank you Craige for informative video. Q:I got a ductless mini split 24 BTU utilizes with piston not EEV is possible to check the refrigerant like central air conditioning? Thanks.
does using a TXV change the seer of the outside unit or is that more compressor efficiency
Hi
Do Piston valve fail ? Do I need to replace it? Mo coil are freezing up after 3 hours when my ac running (R22)
If an evaporator coil gets change does the txv gets change as well or does this part gets removed and transferred to the new evaporator.
I tel my friend you are the best
Thanks!
Again excellent video 👏👍👍👍
Thanks AL!
Just curious....could you attach a thermistor sensor inside the coil in series with the condenser low voltage to shut the system down on low ambient days?....Great videos...I look for to getting them
You could. That is the concept with economizers so that instead of turning on the compressor, it pulls fresh air in from outside instead. Thanks Michael Madrigal!
Very well explained
Thanks David!
@@acservicetechchannel you are very welcome another thing to add on to what I said is that you work very clean and you are very well spoken you are very articulate explaining things but you do not use language that is over complicated which I love about your Channel God bless you and your beautiful family I wish you continued success I will be going to HVAC school January 12th God willing I am missing my right hand but I was born that way and I am also a licensed Barber and a licensed real estate agent in Florida figured I pick up another trade and I always find a way to do the work I also saw how you did the flare on the pipe which is so clean it was so impressive but I noticed that there is a gun that does that for you or a drill I guess you would call it, expensive but I think it would benefit me a whole lot either way sorry for the long winded message encouragement to you my brother keep on being the pro that you are
David, I really appreciate your note and may the Lord Bless you as well! I am glad you are encouraged by the videos and Florida is probably a very nice location for an HVACR tech, thanks again!
touche' my friend..again an excellent video....
Thanks you!
Perfect👍👍👍👍👍👍
Great video.
Thanks Air Mechanical!
Very good!
Thanks Chip!
Great video thank you.
Thanks Ron!
Are all piston universal throughout the different brands even if they look nothing a like? great video.
Most brands will take the ones I showed in the video but there are also smaller versions as well with piston chambers that loosen clockwise instead of counterclockwise. Thanks Channel Cat Chaser!
I disagree with the statement that a txv works better instantly. I usually need to let it run 1-2 hours so that the sensing bulbs eventually loses pressure after being strapped to the suction line before the equalizer and then is open and floods that evap better. I’ve over charged several systems going off subcool IMMEDIATELY after start up. Maybe just a Texas thing since the txv was sitting in a 120f truck and the bulb was pressurized and shut tight
After 10 minutes, you can check the charge with subcooling but still monitor the superheat for diagnosis. The refrigerant is in the system and you can see the levels by reading both superheat and subcooling. As the system runs, the txv lets less refrigerant into the evap since the heat load is lowering. When a bulb is at 120 the orifice inside the txv is more open instead of shut since there is so much opening pressure but yes overall the longer you run a system, the more accurate you will be, thanks!
love the video's as always.
any idea on when you'll put together the video on microns vs. inches of mercury?
I do thank you again for the reminder. I have a backlog of videos in the works, thanks
np buddy,im just intrrested in hearing your view on it.
thanks bud
at 15:54 he said the refrigerant in the TXV was different from the system. I thought R-22 system, R-22 in the bulb. Incorrect?
A better word would have been separated. The refrigerant that is in the system is separate from that in the bulb, thanks and great question!
Will a Trane piston work on a Carrier evaporator?
Which one is better when air conditioning system working in heating mode.
Can you rephrase your question? Not sure exactly what you are asking, thanks!
Do people use Humidifiers in the winter time there? Id like to see a video on Humidifiers. I recently came across a Humidifier installed with an ecobee3 thermostat and both sets of wiring configurations left a new humidifer to not work or work intermittently.
Thank you for letting me know what you would like to see!
hi, if i were to replace a piston with a txv. how would i size it? does new txv comes with a pre-set superheat already? i saw a new txv from supplier bag and it says 18-36BTU. thank you.
How does an overcharged system with TXV effect Superheat/Subcooling and compressor cycling? Does the TXV maintain the same superheat and evap pressure with varying liquid pressure at the TXV?
The txv will try to maintain the same superheat even if the subcooling is high. The compressor amps will be higher and the heat rejection capability will be less at the outdoor unit if it is overcharged, thanks!
Great video. Thanks for the info
Thanks Keith Howard!
Good job Amigo
Thanks Jose!
Love the videos!
I have a few questions.
Do you install or service and Goodman, Amana or Daikin equipment?
I’ve been trying to get a few answers but can’t seem to get them.
I always install TX Valves on my new systems and I always stick with Amana because they have scroll compressors. The Goodman units comes with a rotary which calls for a hard start kit if you were to install a TX Valve on that condenser.
My question is, the 13 SEER unit calls for a TX valve by Emerson which is adjustable. The 16 SEER and higher units call for a TX Valve by danfoss which is not adjustable.
What is the purpose of having a TX Valve that is adjustable? I understand that you need to charge the system based on sub-cooling, but do you need to take your drybulb and wet bulb readings with a TX valve that is adjustable and adjust the valve to that superheat? I wouldn’t say from the factory that they Valve is set to a point where you don’t need to adjust it?
Also when you are checking a system with a TX Valve and you check your subcooling, is your superheat going to be relatively close to the same as your target subcooling? Do you check drybulb, wet bulb to find target superheat and adjust if necessary? Or do you charge only subcooling and call it a day?
So most AC unit TXV systems are nonadjustable. In the case of a TXV that is adjustable, they are usually set close to the normal superheat needed. You would normally run the ac unit and set the subcooling to the correct amount. Then you would check to see if the txv is working properly around 8 to 16 degrees of total superheat. Normally they operate around 10-14 degrees but for a new system install, they may take some time to settle into the correct superheat, thanks!
Your informations are amazing .. 😍
Thanks a lot Muhammed!
can i change txv for piston? R22
hi, so does outdoor temp. affect txv? thanks.
When I step into a new customer's house, how do I know what is used for metering? Should I drill a hole and use inspection camera to looking for it?
Gerry Cui really I hope this isnt a real question....if you think u need to drill a hole an use a camera to see if they are using a piston or Txv for a metering device you shouldn't attempt anything
Here I am removing the doors.
What size of piston should I use for a 4 ton 410 unit?
I know this is an old comment but you should check out Parker Sporlan Virtual Engineer
Another great lesson! What does the other capillary tube go to from the TXV on the upper left, Craig? It looks like everything with TXV is threaded, not brazed, right? Thanks for posting!
The tubing coming off of the txv bulb head is connected to the txv bulb and the other tube is connected to an external equalization port to check pressure at that location. Where the external equalization port attaches to the suction line there is a 1/4" flare. Most manufacturers now braze that line into the suction line. The txv seals on both sides with teflon rings. Thanks
Connections at TXV depend on manufacturer, some are flare others are brazed in. As to the capillary tube on left upper side I have seen coils with sensing bulbs on the coil itself, but it is hard to tell where and how it lands from video. Note that the TXV only uses one sensing bulb to meter superheating though and it it most likely the equaling line.
Just a really good RUclips channel to either brush up on or learn forced air from. Probably the best guy here I have seen, not the only one taking the time to teach for free, but with the amount of professional incompetence I have seen posted as 'Pro's", this guys is top tier. Thanks ACSERVICETECH for taking the time to teach !
so you can replace a piston valve with an expansion valve?
Absolutely as long as you can match up the connections of the new txv. They also make replacement txv's with multiple fittings for it, thanks!
I guess you have to pull a vacuum before you change it out?
Yes recover or pump down, then when the system is at 0psig, replace with the txv, followed by a pressure test, and then vacuum, before breaking the vacuum with refrigerant, thanks
@@acservicetechchannel How much would the whole process cost ?
I was at initial startup inside space was 85 degrees 150psi/390psi 410a super heat was 4 degrees and subcool was at 13 degrees, 22 degree delta t . Why is txv not keeping the 10-15 degree super heat ? 4 degrees is kinda low wouldn’t it ? Please advise thanks for your videos
Seems like the txv is stuck in the open position or the txv is too big compared to the system. Is the evap coil small compared to txv and condensor or is the txv size bigger than the evap or evap and condensor? Also, if it is an initial startup, did the person who brazed it keep the bulb on the suction line while brazing next to it? That would have exerted a lot of pressure down on the txv as opening force. If everything looks ok size wise, I would try cycling the txv back and forth before and while it is running with hot tap water and ice water and switching the bulb back and forth between the cups of water. Maybe leave them in for 20-30 seconds each. You don't want to leave it in the hot water too long as you will not have any superheat for the compressor which would mean sat state refrigerant can get into the compressor. Anyway, those are some thoughts. I hope it helped!
When brazing your line sets and purging the system with nitrogen are there any issues with the nitrogen flowing through the txv, as long as the temp sensing bulb is at a temperature that the valve would see as demand it should be wide open right ?
All comfort cooling txv's don't shut all the way, even if the bulb lost refrigerant, thanks!
Can I use bigger TXV to replace smaller Piston? For example, 5 ton TXV to replace piston on a 2 ton unit? Since the TXV can adjust the refrigerant flow, so it should be able to handle it. Is that right?
Thank you so much for your nice videos!
no txv sizes are still needed such as a txv that has a range of 18,000btu to 36,000btu.
@@acservicetechchannel Thank you for your quick response. One more question, are the screw caps compatible on piston and txv? If not, I have replace the cut off small tubing on the other side of distributor? Thank you again
I HAVE PISTON CAN CHANGE TO TXV R22?
If a system is installed with a piston from the manufacturer, can you add a txv? Can txvs be added to any systems that have pistons?
Usually a txv from the same manufacturer will fit onto the part of the piston chamber once the piston and front of the chamber is removed, thanks!
AC Service Tech LLC thanks for your swift response!
Glad to help Henry!
My Air conditioner turned of because making height pressure on heating mode .
That sounds like your indoor airflow is not high enough or there is some blockage since you are absorbing heat outside but not able to reject it inside, thanks
So, the TEV should be installed vertically to work? Thank you
It would depend on how the internal bypass is built but yes you are safe if the head is towards the top, thanks
Thank you so much for your help,as I am currently going to school for HVAC.
Does it matter if a txv mounts inside or outside the coil cabinet? I have a New Goodman with an A coil and removing piston and adding txv before install.
It does not matter but if it is outside, the txv must be insulated because it will have low temp refrigerant running through it so it would allow condensation of any humidity, thanks!
AC Service Tech LLC Good deal and thank you for getting back to me. It’s a Goodman TX3N4 and comes with a round insulation cup that fits the txv and velcro’s shut.
If you have a txv and the blower quits running it will still freeze up.
Yes the txv typically is not able to shut down completely but it lets a lot less refrigerant into the evap than the piston. That is much better for the compressor in terms of how much saturated refrigerant is entering into it, thanks a lot Kevin
So my question is do i can replace txv for a pisto
I only replace piston with a txv for efficiency and compressor safety. I think some people take out txv's and replace them with a piston because they don't understand how txv's work maybe. They are pretty reliable and worth keeping, thanks
AC Service Tech LLC thank you l installed a txv and its working good
Hi! How do I recalculate/recompensate for the lost oil xoes goes with the refrigerant on recovery? Is there any mathematical formula to determine jow mu h oil is left on the system parts after the recovery?
Actually it is very hard to determine that unless you have an oil separator in the line like car type recovery units. This is since you can't identify if it is oil or liquid refrigerant weight in the bottom of the recovery tank. There is much more oil in a split system or packaged unit than in a car. For the most part on a standard system that has not been recovered more than once the oil level should be adequate after recovery still.
acservicetech, thanks for responding. Right now, Im working on my car and I lost my refrigeration through a leaking core. I forgot to put back the cap after used the gauges (where I found both pressures are loe) and my A/C wont run in the morning. Any advice.
There is usually a low pressure switch that will not close allowing the system to turn on unless there is a some refrigerant in the lines, thanks
acservicetech thanks
Excellent video. What do you recommend to seal the threads on a fixed orifice and TXV? Ive seen cases where a system is low on refrigerant and the nut is tight but the leak is from the threads. Do you recommend leak-lok on these?
Typically the leaks are not coming from the threads but the seal face. A teflon ring is used near txvs or a flare with refrigerant oil or something like nylog is used but only on the face of the seal. Thanks!
People still use pistons because they are cheaper and more reliable.
Thanks na na!
Kind of like a carbeurator vs fuel injected. The Car computer keeps the air/fuel mixture perfect no matter what temp and it works great until it fails.
Seems a TXV does a similar job as it keeps the amount of refrigerant that passes through at a perfect level based on temperature.