How to diagnose a Variable Displacement A/C Compressor

Learn how to diagnose a vehicle's A/C system that uses a variable displacement A/C compressor.

[@FisherCatProductions]

Interesting. The best explanation I've heard of the relationship between the gauges and what is actually going on in the system! Thank you.

[@wisdomspitter7688]

That is so helpful. Thank you Sir.

[@Palm18]

Excellent! Thanks!

[@scottcampbell1552]

I love the videos showing the pressures and duty cycle under different conditions. However, can you please include a video of a variable displacement compressor with a mechanical control valve? I see lots of discussion of the solenoid type and the ability to test the signal/demand, as well as videos on replacing them because of a high failure rate. I have an Altima (R134a) with a Valeo DCS171C variable compressor with a mechanical valve (manual climate control) that works on pressure. I'm having issues with getting good cooling and have above normal low side and below normal high side and suspect the control valve is not functioning properly (last year replaced evaporator, TXV, dryer and pressure switch). With ambient about 84 I had 45L and 150H. The pressures tell me the TXV isn't stuck closed, and it's slow to equalize when shut down so I don't think it's stuck open. The low side pressure takes a minute to begin dropping after turning the AC on. I wonder if the bellows in the valve has ruptured and the valve is in a sort of neutral failed state (maybe a 50% position?), allowing for some compression but not changing based on demand (a low side pressure increase due to heat load at evap.). A video on troubleshooting this type would be great, helping to distinguish between the mechanical valve and other possible sources of trouble.

[@ProfessorPentane]

Hi Scott, if the compressor is not at max Wobble plate angle, the low side should be a little high and the high side a little low. The more straight (up and down) the wobble plate, the more the gauges will read the same pressures, (low side high and high side low). The manual control valve is hard to diagnose because you can not control it like the newer EVDC ones, but the gauge readings will be the same between the manual and electrical control compressors if the wobble plate is not moving correctly. I hope it helps and be sure to subscribe to the channel. PP.

[@relmdrifter]

Thanks, these are new to me!

[@ohenenorb]

Very good explanation of how the variable displacement compressor works. Question: Is variable displacement compressors used only in a vehicle that has climate control system type of air conditioning?

[@lwilliam22]

great stuff. help me a ton

[@lupedel-r5p]

SCOT , LOVED THE INFO . I HAVE SUBSCIBED AMIGO . MY SON HAS A 2019 IMPALA , I THINK HIS IS RUN BY MODULE . HOW DO YOU TROUBLE SHOOT THAT, MY SMALL SCANNER SAYS CLUCH ON BUT NOT SPINNING AND IT SAYS NO REQUEST ON COMPRSSOR BUT ITS ON AUTO W/DIAL ON LOW . DO YOU HAVE A VID ON THAT SIR ?

[@peterdrury5627]

Hello Professor Pentane. I was surprised to see the duty cycle on the PWM control still around 40% when the A.C. was turned off. Would this not possibly point toward a potential error on the PWM controls, which I would have expected to go to zero? If this is normal, I would hope for some discussion on this in your tutorial. I also noticed that when you initially displayed the compressor, you stated that it was a clutchless compressor. Near the conclusion of your tutorial, you stated that the compressor clutch had disengaged. Is it possible that PWM strategies would differ between the two types?

[@bamwa]

Good video. Can you replace the solenoid only if it is acting up?

[@ProfessorPentane]

On some compressors, yes you can only replace the solenoid. Check for parts available.

[@hill_customs6807]

So im assuming with this type of compressor if the ac is on but freon levels are even and not moving the compressor is bad . Or is there a chance that the variable compressor wobble can be at 0% ever. Working on a Hyundai with a clutchless variable compressor.. fuse is good. No errors in the ecm with the ac system. When Activating the ac button freon levels just stay static..

[@ProfessorPentane]

Yes, it could either be a bad compressor or an electrical issue the computer can not detect. Can you command the duty cycle of the compressor with a scan tool to see if it changes?

[@hill_customs6807]

@@ProfessorPentane I don't think my scanner has the capability to do that with the duty cycle or at least I can't find it in there anywhere..

[@ProfessorPentane]

@@hill_customs6807 You can you a voltmeter like I have in the video and back probe the control wire going to the solenoid. If you are seeing voltage change, the control side is probably good and you have a bad compressor or solenoid. The solenoid should be around 10 ohms.

[@ungoofaaruregionalhospital5189]

thnks

[@benjamin-rw8qm]

what speed the blower fan was during this test?

[@ProfessorPentane]

I started off with the blower fan on high and towards the end of the video, I switched to low speed to get the duty cycle of the compressor to drop due to the evaporator getting too cold. Thanks for watching, PP.

[@leonelcontreras1851]

What Fluke model is that tester? How do you have it show percentages? I tested mine and it only showed decimals on my percentages.

[@ProfessorPentane]

I use a Fluke 88 that has the HZ option.

[@dangrbitch]

I got an ac with one of those compressors. The system has no leaks and did a full recharge. But it only cools at low rpm like at idle. When I start driving it stops cooling Can that possibly be a simple fix or do I likely need a new compressor?

[@friesy3518]

Did you ever find the answer to this? I'm having a similar problem with mine... It's only cool when sitting at idle. The vent temp gets higher when driving at highway speeds.

[@afeezemokpaire]

​@@friesy3518were you able to fix it

[@eddiemiles1920]

Low charge maybe?