Liquid Line Temperature
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- Опубликовано: 7 июл 2024
- Bryan goes over the basics of liquid line temperature. He explains how we measure it, what it can tell us, and what appropriate ranges tend to be.
We typically measure liquid line temperature with a temperature clamp outside at the condenser. Normally, the liquid line temperature shouldn't change very much; even in cases when you have exceptionally long line sets or if the liquid line has been routed through hot areas, you shouldn't see much more than a two to three-degree difference throughout. By comparison, the suction line has a lot more variation from start to finish.
The liquid line can't be any colder than the medium to which the condenser is rejecting its heat (the outdoor air). In other words, the liquid line can't be cooler than the outdoor air in a traditional residential split A/C unit. If the liquid line is colder than the outdoor temperature, check to make sure that your probes are in the correct places (e.g., not in direct sunlight).
If you detect a significant temperature difference or if the liquid line is colder than the outdoor air, you may be dealing with a restriction between the condenser and wherever you're measuring. Restrictions may be in the line itself, in the liquid line service valve, or in the liquid line filter-drier. Elevated liquid line temperatures may indicate a restricted condenser coil or overcharge.
We can determine the appropriate liquid line temperature range by looking at the condensing temperature over ambient (CTOA), which is the difference between the condensing temperature (saturation inside the condenser) and the outdoor ambient temperature. Older systems tend to have higher CTOA, and newer high-efficiency systems tend to have lower CTOA.
Comparing the liquid line temperature to the ambient temperature is called the "approach" method. The absolute highest temperature that the liquid line could be is the CTOA, and the lowest it could be is the outdoor ambient temperature. To find out what our liquid line temperature should be, we also have to look at our subcooling. You can subtract the subcooling from the CTOA to get your ideal liquid line temperature. Of course, there is some guesswork involved in this method.
If the liquid line temperature is much higher than expected, then it may be time to connect gauges.
It's also worth noting that refrigeration systems will often have higher CTOA than HVAC systems. However, we're also trying to reduce the condensing temperature to reduce compression ratios and get more efficiency out of our systems.
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/
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I especially appreciated this episode, thanks.
THANK YOU!! I am not an HVAC technician and do not have plans to become one, just a DIY homeowner. I thought my liquid line felt "too hot" and crawled over so many forums that turned me in circles. Your video summarized and explained everything so simply in 11 minutes! I'm glad I found your channel as I will return to it in the future.
Glad I could help!
Been doing HVAC for a few years now and I still am learning new things everyday thanks to you!!
Extremely helpful to me. Thanks for bringing this episode to us.
Me and some other students worked on a remote condenser that was just... burning radiant hot. We had a lil' fold out canopy. It was a HUGE life saver. Not even measurement taking, just being able to get inside the fans to clean them without burning our arms. Radiant is no joke.
9:35 - One small quibble: As I'm sure you probably know, Lennox uses (used) approach method charging, which is awesome. The instructions specifically say, "add refrigerant to lower the approach temperature or recover refrigerant from the system to increase the approach temperature". Indeed, I recently serviced a unit with a bad capacitor and after replacing it, I checked and found the approach temp to be around 1°F. So, following the instructions, I recovered just over a pound of refrigerant, to bring the approach temp to exactly 6° as called for.
Aside: The homeowner told me she had it serviced the previous year by a tech that "didn't seem sure whether it needed freon, so he added some to be safe". Sounded like he was looking for a subcooling number, which isn't provided on these units. Using the traditional subcooling measurement, it showed about 11°F before I removed the charge, and about 6° after. So, not too surprising to find it overcharged from "guessing".
EDIT: Awesome video otherwise. I love these theory discussions - they make us all smarter! :-)
i am not sure how approach and subcooling do not follow each other. i thought they were two methods of getting to the same thing.
I just bought that field piece set so I can start checking stuff out. I like the little facts that only come from a pro that has teaching skill. Teachers know the details help to make it fun learning.
This was a great episode. Thank you!
Bryan Thank you for your time&videos it helps me tobe a better tech.
This man is a master HVAC TECHNICIAN and instructor
I just tested these numbers with my Testo 550 and it's absoultly correct!
I'm amazed.
thanks!
Thank you. This is a wonderful explanation and very helpful to gaining another quick way of checking out a system.
I don’t know that we even talked about sub cooling in my trade school in the late 80s.
I always learn something new from your videos and they clarify concepts and techniques. Have you considered having a formal online hvac trade school? I think the course content is already present in your videos. You would just need to sequence them and add questions.
Some of the questions could come from your current fans and followers about actual on the job challenges.
Sometimes the issue could be ethical concerns. Once I directly told the customer why a motor had failed who was looking over my shoulder while I worked on it. A previous technician had shorted the leads together in a wire nut that we’re not being used for the different motor speeds and that burnt out the new motor. Technicians in my shop were upset that I had not made up a story to cover for that mistake. I believe that honesty is the best answer even though it has cost me my job a few times. I moved on to something that was more suited to me and was more beneficial financially. So even though at the time the results of being honest seemed to be bad, in the near future it really worked out for the best!
Perfect. Made so simple!
Excellent explanation about subcooling, but it is important to mention that the subcooling calculation only applies to equipment that has a TXV.
For charging purposes.
But it's always good to take a peek at the subcooling on any system
Good stuff! Thanks for posting!
The term “gauge up” should not be taught. Every time you put gauges on a system you loose refrigerant. If this continues you will find the system low on charge and start looking for a leak that doesn’t exist. This is especially bad on package units. My gauges are the last tool I grab for diagnosing. Very good video. All techs should watch and learn from this video.
Thanks Mr HVAC Great Video.
Excellent video THANK YOU
You are a fantastic teacher and communicator.
I totally agree. Industry changer
I LIKE YOU A LOT,YOU VERY KNOWLEDGEABLE HUMBLE PERSON👍👍👍👍
It is instructive to note that long lifts (vertical rises) can hamper subcooling at the throttle or expansion valve. This is one reason many small refrigerator/freezers will skimp on the metering device, while helping to ensure good subcooling by using a makeshift heat exchanger consisting of a capillary tube liquid line inside or alongside the the suction return line. Kind of an ingenious design to cut cost, if you ask me.
Long lifts can cause the liquid to flash enroute to the evaporator, we see that a lot in Arizona. The quick fix is to route the last 6 feet of liquid line before the evaporator inside the suction line insulation and taped to the suction line. That amount of cooling will help keep the freon in a liquid state. Don't fall for the trap "if a little is good, a lot is better." Never do more than 10' of this mod or your freon can get too cold to proper vaporize and you can flood the evaporator.
Wow great thinking, I feel this could be useful for commercial refrigeration too. Often you don’t even have a service port to hook up to and if you use a piercing valve you really shouldn’t just leave it.
I am listening and learning
excellent Tutorial..Thanks for sharing..
Great job and video like always
Thanks, very good information .
Great videos. Thanks 😜
Excellent info!
agree brotha
Hi, I want to say thank you so much for sharing the information . I know about the time but you speaking very fast. Thank you again
I noticed that small units like those used in railroad locomotives under the cabs or on the roofs as well as rooftop RV units and even window units run somewhat higher high side temps than your typical home units do also. I work on the HVAC stuff no one elses wants to work on per say and it pays well enough for me. No big business here just me and my education, but I do have a pretty decent contracts with a couple railroads and cellular carriers for HVAC here I also work on IT and communications as well.
Amazing lecture. Thank you. raphael nyc
Thank you!
So awesome
Lennox has lots of condensers looking for 3 degrees of sub cooling. Now measurequick is always telling me my liquid line temp is too low. Radiant heat plays a big factor yet most Lennox xc17-25 subcooling is 2-6 degrees. If I charge the system to manufacturers specs I get a 20 degree split on evap coil.
The HVAC Hacker are you adjusting the expected sub cool in the app?
I use the feildpeice wireless with the app. You can put in the sub cool or super heat on the label and compare it to your current reading. If it above or below by 2 degrees you will get a warning.
Same thing with the psychrometers. It will take the wet dry and humidity and give you a cooling target depending on the data.
I service a lot of Lennox units in SWFL and the sub cools vary widely I agree.
Brian Orr has the answer 🤔 . All is about the weather conditions and the temperature of the particular area with the sun latitude to earth and also with how cool you like to have your conditioning space. 😀😁✌🤣🤣🤣🤣
Great video!
I thought it kind of odd the copper was not cleaned before attaching the temperature clamp.
Did I miss something?
You’ve probably noticed RHEEM Classic package units don’t have access to the copper unless you lift the grill and place the clamp.
Doesn’t that effect the measurement because of the added heat from the condenser?
Again thanks for all the great training!
Rick
Thanks from Bangladesh.
Ty great video
His name Bryan, not Ty
Hi Bryan, is this applicable in fixed metering device? Thanks!
I came home today and my inside temp was 80. The outside temp was 90. I could hear the fan running. I left the temp set on 75. I drop the stat to 72 and then back up to 75. I then went outside to the condenser and hot air was coming out the top. The large line was cold and the small line was warm. I went back in the house and now the temp is slowly dropping.
Nice video slow fan can go along with dirty condenser or over charge
👍👍👍...can you please make a vedio about the suction line pressure when its getting too hi!!!
which smart probes do you consider best and why
Hello Sr. First. Great video. Very precise and professional. Could you please tell me After what year or date is considered modern equipment ?
Thank you for the video. I have a question. Why my subcooling following together with the liqid line temperature. I’ve replace txv to 410a. I did convention from r22. Put filter liquid drier. Basically I’ve left the old evap coils and just replaced condenser. 14 seer. 2 ton old coils, 2 ton r410a condenser? SH 22 degrees. Adding more refrigerant- liqid saturation temp same as liquid line pipe temp. Sustem works fine. Why I can’t get any temperature differential on high side?
Replaced a mini split today and after firing up, noticed the liquid line cold and sweating. The line set is only about 8' long....right out the wall and to the ground to the condenser. Pressures showed perhaps the unit being a little over charged from the factory so recovered some of the 410 and got that to an acceptable range. The unit cools great and we got great temps inside but just found it odd that it was that cold. Any thoughts?
Good stuff! Given compression ratio directly relates to efficiency, this leads me to the question of why not use the largest expansion orifice possible?
🤔🤔🤔😬🤪😂😂😂😂😂😂
Tnks from Miami Fl. 😎
They don't make tanks in Miami. Most of them are made in Detroit
Thank you for sharing this video. I very much appreciate your sharing it. How did you come up with your highest condensing temperature? I know that you are guessing at it but still, there must be something that you use to come up with the guess. What is the relation between the SEER rating of the unit and the target cooling? If you run across an old unit with no information on it how do you know what the subcooling should be? Would that also be a guess based on its seer rating?
We estimate CTOA based on SEER - I’ve done a few articles on this but will be doing a CTOA specific video as well
Gracias che
Liquid line cold before dryer filter when system turns off . Help
I tried this method at work today. I was servicing a 14seer 6 year old carrier. 85 degrees outside, so the condensing temperature should be 105°F. Manufacturing label says 10° sub oil is required for indoor txv. Liquid line should read around 95°F. It read 92.6°F so I technically by this formula have a 12° subcool.
However, I use analog gauges and a Fieldpiece meter with a thermocouple clamp. According to my tools, I found I had 305psi in the high side and read about 3° of subcool.
I trust my gauges and meter more than a new technique I just discovered,, but I’d like to know where or how did I go wrong? I’m assuming it’s the condensing temperature being off. If so, where or how can I find that?
Hi, I have an unsolved problem. 2 tons split unit heatpump, liquid line temperature is 63f (sweeting), sat 60f. suction line 37f, Sat 32. outside temperature 73f, interior 76. I think is a restriction so I have replaced the dryer cause 6f diff but the problem persists. maybe the capillary tubes in the condenser?. Why a have a lot of liquid in the evap? Could the three-way valve cause this problem? I think not but some technician suggested that. I recharge right amont of r410a.
can you help me? Thnx
Did you ever solve this?
If you didn’t live so far I would work for you just to learn!
Is it possible that liquid line temp can be higher than liquid saturation temp and if so what does it mean ?,i saw that on a trane residential unit recently and was unsure i have never seen that ,all help greatly appreciated
So does the Seer apply to refrigeration units?
If you had an over charge, the liquid line temp would go down, not up, due to the excess subcooling of the refrigerant stacked up in the condenser. The amount of subcooling you need for a particular system is the amount that will deliver a solid column of liquid to the metering device. This varies dependent on liquid line pressure drop due to fittings, accessories, lift etc.
You wrong liquid line temperature goes up! You can try it 😉
Generally 100. Good way for me to judge
Had a brand new HVAC system installed. One week later blocks of ice all over the lines. Installer “fixed it” and it ran the rest of the summer. Had a second company come out and found “reduced superheat, elevated sub-cooling, reduced airflow due to lack of returns and refrigerant overcharge.” First installer says “It’s running fine, every system can be installed differently.” What should I do? Thank you.
Hi, good info.
My mini split isn't creating the chill effect anymore and it's taking hours to drop a degree even at night time when ambient temp outside is mere 84°f. I checked everything as far as i know, suction pressure is good R22 66 psi, grille temp is 53°, suction line temp is 48°, then i checked my liquid discharge line temp and it's actually lower than ambient temp 68° and cold to touch! could this be the issue of slow cooling? I haven't checked discharge pressure since there's no service port in discharge valve.
Metering device is in the outdoor unit on the mini splits, so you "liquid line" temp is going to be lower. If you suspect the charge is wrong the only way to properly correct it is to recover the refrigerant and and recharge it by weight. You cant charge the mini split with sub cooling/superheat method.
Is there a video like this for the suction line temperature??
jonas pratt I would like to see a video like that.
The best temperature you can take is at the register and return. If I'm getting 15 to 21 degrees I don't hook my guages up. Of course the load on the system is taken into consideration. Time is money when you work for a contractor. Blow your guages out regularly and use low loss fittings. I'm more concerned about hooking up guages when I work on small refrigeration systems.
Hello there , i have seen many systems that the filter drier had been installed inside close to air handler, is there any difference between install it outside and inside? Thanks
How do you establish "Target" subcooling.....from manufacturer?
Do package units have seer information?
Ambient temp 110-115. HOT! The line coming out of the compressor into the coil is almost too hot to touch. The liquid line entering the house is also hot but not as hot as the condensing coil. How hot is too hot when it's 110 outside? I'm not sure if I am undercharged, overcharged, have air in line or restriction somewhere. Most techs blame TXV. Suction line is barely cold while running. Actually suction line becomes nice and cold right at start up but then warms up soon after.
How hot should a compressor be when running
You mention Over charge increasing LL temps twice (Do you mean discharge Line?). The more refrigerant backing up against the meter, the slower the velocity, the more time spent in the coil, the cooler the line temp? The less (to a volumetric point) refrigerant in the system, velocity is increased, less sub cooling, less heat can be rejected, you will see higher line temps, again at a volumetric point?
Have I got it wrong, Have I been seeing this wrong for 30+ years?
RJ_Make no you aren’t wrong. I’m going to remove those references.
Where do you find the Target Subcooling temp (in your case 13 degrees)?
on the dataplate on the condenser usually
What would you expect the liquid line temp to be on a 21 Seer 2 stage unit that’s running on 1st stage with absurd airflow, and an oversized evaporator? I’m getting 2-3 degrees below ambient right off the coil, no appreciable change down the short lineset.
Some systems have a heat exchanger on the liquid line that can drive down the temperature below ambient. I suspect its for a tiny boost to efficiency and cooling capacity.
.
Will overcharged make the vent outlet not as cold as it should be.
I have a 3 ton, R-22, SEER 11 unit that routinely has a LLT of 130+ degrees on a 95 degree day. The coil is clean and it has good air flow, I can't figure this one out. Would a liqiud line restriction at the evap coil cause this?
Why don’t you write a book?
Vrey writing all detal book fee
So will recovering the refrigerant, blowing system with nitrogen and pulling a vac clear a restriction in the condenser? My liquid line is cooler than outdoor temp. It's a 9 year old 410 with txv so I'm considering just replacing it again but rather not if doing the above will clear it?
What system do you have?
Some mini-splits have a suction to liquid line heat exchanger or some other set up that drives down the temperature of the liquid line and can even lower it below ambient. This adds more subcooling and gets a bit more efficiency out of the system.
2nd question. Are you sure the restrictions is at the TXV vs at the filter drier? If its the latter, no amount of nitrogen is going to unblock it.
If its the TXV, then why is the TXV restricted? Is it debris clogging the screen? Is the TXV stem jammed? Has the sensing bulb loss its charge? Is there a pressure equalizing line? Is it choked/kinked?
@@WarriorofCathar it's a typical 3 ton split system. I was thinking the restriction was in the condenser itself because of what he mentioned in the video. He mentioned if checking the line temp at the condenser and it was lower than ambient, the restriction is in the condenser
You mentioned that an overcharge would raise the liquid line temperature. Wouldn't this be the opposite as an overcharge would increase the subcooling to the point of outdoor ambient temperature? A severly undercharged system would have a cooler than expected liquid line. Would you possibly have a video or demonstration that would show how overcharging would raise the liquid line temperature?
It’s one of those things I said that I really shouldn’t have without a lot more explanation. I’m going to cut that part.
@@HVACS Now that I thought about it more, would it be that an overcharge would be moving more heat than the condenser could reject? I wouldn't say cut it from the video, it is good to know some of the tricky things.
I see an E/V RE20 microphone...in former life, were you a "radio guy"? Sounds very good, what I would expect from the classic mike.
I came across a 5 ton package unit where the liquid line was about 120 deg F the outdoor temp was about 95 deg F even the compressor was to hot to the touch could the TXV be restricted?
Matthew Mccullough never the txv lol
Well then Sal what could it be
“Correcting power factor” next? 😬
Where did you find that targeted subcooling?
It's printed on the data plate
I though overcharge made you have a higher subcooling so the liquid line temp would read lower? Assuming a clean condenser, evap, filter, etc.
Most of subcool comes as you drive up the condensing temperature. It’s sort of a bell curve.
@@HVACS Thanks for the reply. That's where the outdoor air temp and amount of sun beating on the coil comes into play I assume.
Yes, in general overcharge doesn’t drive up liquid temp as you stated, but because charge is often used as a compensating factor for the true issue it can be tough.
You say the liquid line temp shouldn't change much... maybe picks up 2-3 degF, and then go on to say ....especially with long runs that may take you through vertical sections and hot attics. Allow me to ask for clarity. I have the entire liq line "bare", ( as is common), and it runs maybe 4 ft length between the outdoor condenser and the house.....then runs up inside the house wall ( say 12 ft vert rise)....and then enters the attic space for another 18 feet before it enters the air-handler section in the attic. The attic atmosphere gets to above 122 degF on a 91 degree day. I want to insulate the liq line in the attic space, yet leave the outside section bare, to help preserve the subcooling in this line before it hits temp valve in the air handler. Comments?
👍👍
Hi, I am from Poland, so i got use to Celslus or Kelvin scale, I guess you are dealing with Fahrenheit scale in terms of absolute temperature context. But if you are saying that some temperature is greater/less by some number of degrees, is this number also in F or K ? Im trying to understand this numbers but as per these units have diffrent gain and offset factor, it's even harder to convert these numbers :-) Thanks for help.
So the liquid line shouldn't be any colder than the air temp. But in FL it rains a lot and if you have had a shower recently and the condenser coils have gotten wet, wouldn't that then make them subject to "wet bulb" cooling and potentially have the liquid line cooler than the ambient air temperature?
So I have a 5 ton roof top unit that is cooling intermittent,, my gauges read 65 psi on suction line and 200 psi on liquid line with liquid line temp at 165 degrees,,, I washed condenser coil with no change on temp?????
Its an r22 system
So the compressor is going off on thermal overheat..
What is the reason of liquid line temperature to be around 20c ? While outdoor temp is around 35c
What system are you running? It could be a restriction or it could be the design of the unit. Some units like Daikin and Mitsubishi have a heat exchanger to reduce the liquid line temperature below ambient to slightly improve efficiency. You'd had to do a more detailed analysis than just liquid line temp to figure it out.
Make up a "Loli pop" gauge, a gauge with a quick coupling, very little refrigerant loss.
i used my fieldpiece probes with a low loss fitting. it has no hoses.
@@Papasquatch73 what's a setup like that cost?
Yesterday after cleaning the condenser coil, I took the temp of the out going air from the fan. We had outside air at 100° and the temp after the fan was 112°
The fan motor had low amperage draw and the compressor had low amperage draw. It was a 1993 Lennox Split System and I recommended replacement of the whole system. I just do Service and repair. No installing. Honest assessment.
Head should be 30 to 35 Degrees above Outside Ambient Temp(on your gauge). KELLEY
P.S.. When done front seat the Schrader valve on the high side,and sock the High side liquid into the low side,minimizing refrigerant loss.Kelley
Not sure how you came up with a recommendation to replace the whole system other than the fact you make commission on your "honest assessment" repair.
@ 5:27, You have me all confused. Say an ambient of 80 degrees. Saturation of 95 degrees. 13 degrees subcool, you should see a 82 degree LLT. Approach would be 2 degrees.
Now lets say the subcool was measured at 4 degrees, 95-4 = 91 degree LLT, and an approach of 11 degrees. Am I to understand that due to this approach nearing 15 degrees above ambient, I should remove refrigerant?
According to Carrier, you would add refrigerant to lower LLT. A higher LLT means a lower subcool.
Window ac compressor normal running tempreture ???
Always.
What was the line temp?
ruclips.net/video/XClJ74NQx20/видео.html looks like 97. his outdoor temp was 92. i think he bumped the outdoor temp up to 95 in the example so the math would be easier for the viewer to follow along
But how can we applly this metheod with the out door capullary sysyem
Just hit the "apply" icon. Happens almost immediately
What other refrigerants hit a transcritical state like co2 does??
LG and Samsung
my outdoor unit is always sweating and the AC techs dont know why, they say bc the air handler is a different brand...could it be bc the the temp of the line is too cold? if so, how is this fixed? thanks
Air Handlers sweat depending where they are installed sometimes. If its hot and humid then they sweat.
I always sweat when I go outside and it's hot. So is it the condenser or the air handler?
@@jimwhite9483 condenser
I'd be cautious about the liquid line always having to be above ambient. 90% of the time, yes.
Some mini-split manufacturers have models with either a liquid line to suction line heat exhanger or some other device that adds in additional subcooling and can drive the liquid line temp below ambient at certain operating conditions.
Daikin VRV-A and Mitsubishi Mr.Slim for those interested.
He specifically stated this is for residential A/C, not mini splits. He also mentioned that if the liquid line temp is lower than ambient, there may be a restriction of flow, that would be the TXV in the mini split.
some of us are retired with just gauges at hand ,,,,nothing like the kids use today all digital gauges all decorated nicely with numbers ! and old techs that only use their own tools just to maintain their own home equipment will most likely not buy all this fancy new equipment we where shown in school to add it all up without i phone etc etc etc ,,,,,,i am 66 myself just for the record ,,,,,,
3 degree what? Celcius or farenhiet?
Direction as verified on a compass rose
Bryan, hi many moons ago , I was with a guy having \problems\, he read the charging chart for that brand, but did the OPPOSITE. To the instructions, I watched him do what he did, and asked WHY ! He needed to so superheat, but was doing sub cooling, told him to RE READ THE TABLE & instructions , simple as that ., I think it happens often enough . Cheers 🇺🇸🇺🇸🇺🇸🇺🇸
I had to slow the play back speed on this guy
Bill Hamrick he reminds me an HVAC Mac Lethal
So you’re high side pressure in that scenario should be 327 I think lol
dirty condenser will increase temp