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.
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I especially appreciated this episode, thanks.
I LIKE YOU A LOT,YOU VERY KNOWLEDGEABLE HUMBLE PERSON👍👍👍👍
How hot should a compressor be when running
Will overcharged make the vent outlet not as cold as it should be.
You keep repeating yourself and going off on tangents
Should have been a one ☝🏻 minute video
Good knowledge sir
Love you sir 💖🇮🇳
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?????
It would be so nice if you could include the metric system. Less than 4% use imperial.
How do you establish "Target" subcooling…..from manufacturer?
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?
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
What other refrigerants hit a transcritical state like co2 does??
But how can we applly this metheod with the out door capullary sysyem
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.
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?
dirty condenser will increase temp
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?
👍👍
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!
Window ac compressor normal running tempreture ???
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.
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?
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?
Good stuff! Given compression ratio directly relates to efficiency, this leads me to the question of why not use the largest expansion orifice possible?
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
Great job and video like always
Thanks, very good information .
Thank you!
Do package units have seer information?
So does the Seer apply to refrigeration units?
Perfect. Made so simple!
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.
I just tested these numbers with my Testo 550 and it's absoultly correct!
I'm amazed.
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 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.
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.
Hi very informative video. I recently noticed that when the a/c unit ,of a friend, started working the liquid line, the thiner copper pipe coming out of the condenser, was sweating. That is to say it has moisture condense on it, and it felt very cold to the touch even though it is summer. Does that indicate a restriction or a low level of refrigerant?
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
Liquid line cold before dryer filter when system turns off . Help
What is the reason of liquid line temperature to be around 20c ? While outdoor temp is around 35c
3 degree what? Celcius or farenhiet?
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
Sorry but u give too much info for something simple. Old guys knew there hand was 98 so line would normally be slightly warmer . All your info is true but for a new guy all he needs is basic temp he is looking for . Condensers are normally based on 105 cond temp at 70 to 80 ambient. So liquid line should be roughly hand temp. Too or cold you have issue .
So awesome