Cannot get compressor to engage

Friendly format provided to inquire about automotive a/c systems.
Archived Forum

Moderators: bohica2xo, Tim, JohnHere, Dougflas, HECAT

User avatar
JohnHere
Posts: 294
Read the full article
Joined: Sun May 13, 2018 10:20 am
Location: South Carolina Upstate - USA

Re: Cannot get compressor to engage

Post by JohnHere »

Your car is very complex with redundant electronics controlling just about everything, including the A/C. You found a leak for sure at the compressor that needs to be addressed. But that doesn't explain why the compressor won't start as it should while charging the system through the low side.

It could be as simple as too wide a clutch gap, a bad pressure switch, or something obscure like a faulty control head in the dash failing to communicate with the A/C amplifier, which could also be bad, and in turn commanding the compressor to turn on.

I don't recall anymore, but have you checked the clutch gap with a feeler gauge? On most vehicles, it should be about .020". Smaller than that is okay as long as the clutch plates don't drag. Greater than .020" and the clutch might not engage, just as you're experiencing. Try getting a feeler gauge in there to measure the gap. Some people use a business card for that purpose as well.
Al9
Posts: 246
Joined: Tue Mar 10, 2020 3:26 am
Location: Southern Europe

Re: Cannot get compressor to engage

Post by Al9 »

A bad AC clutch harness can do that. I had the same issue on my car and you had to yank the ECU side AC clutch harness to bring the clutch back to life (stopped working randomly on bumpy roads). Needed a new harness to be spliced in and has operated fine ever since. No amplifiers or any fancy stuff at all on my car; pulling the heater knob sends a signal to the ECU and the clutch gets energized, provided that the coolant is cool enough (you want an overheating engine to have as little load as possible), the RPM is high enough (a compressor can stall a barely running engine) and the liquid line pressure is high enough (too cold weather or too little refrigerant, and compressor oil return stops) but not too much (don't know the values, but there's a pressure transducer on my liquid line and the wiring goes to the ECU harness).
Beamer.619
Posts: 10
Joined: Mon Nov 16, 2020 4:18 pm

Re: Cannot get compressor to engage

Post by Beamer.619 »

So I installed the new pipe pulled a vacuum for 2 hours then started to fill the system with refrigerant and I saw the compressor engage for about 5 seconds then turned off so I took the relay out and bypassed it with a wire so the compressor was running right when I started the car so I started filling the system with the rest of the bottle of refrigerant and took most the bottle then the belt started slipping on the compressor and made a loud screeching noise and then the compressor clutch shut off so I turned off the car. I then pulled the wire out and put the relay back in the car and tried the running the compressor it tried turning on but the belt kept slipping for about 3 seconds and then it gave up and just wouldn't engage. What could my issue be so far I haven't see anymore leaks from where it was leaking from.
User avatar
bohica2xo
Posts: 839
Joined: Wed May 11, 2016 4:12 pm
Location: Las Vegas, NV

Re: Cannot get compressor to engage

Post by bohica2xo »

And the good old jumper wire kills another compressor.

That little wire sells a lot of parts. No you get to guess how much of the compressor metal went down the discharge line as it ground to a stop.

Your compressor is seized from a lack of lubrication return, Running when the system said it should not.
Al9
Posts: 246
Joined: Tue Mar 10, 2020 3:26 am
Location: Southern Europe

Re: Cannot get compressor to engage

Post by Al9 »

I can't stress this enough, going to a pro is always cheaper than a new comp. Charging with the comp on is a huge no no.

That poor comp was likely on its last legs anyway. The swashplate half-shoes are designed with great abuse in mind.
Beamer.619
Posts: 10
Joined: Mon Nov 16, 2020 4:18 pm

Re: Cannot get compressor to engage

Post by Beamer.619 »

I got a new compressor, expansion valve, and drier the car was retrofitted in 2000 from r-12 with mineral oil to r-134a with ester oil. I'm doing a full system flush and replacing everything except for the condenser and evaporator my question is should I use ester oil since that's what they used when they retrofitted it or should I use pag oil.
User avatar
JohnHere
Posts: 294
Joined: Sun May 13, 2018 10:20 am
Location: South Carolina Upstate - USA

Re: Cannot get compressor to engage

Post by JohnHere »

I advise replacing the condenser as well because that component acts as a filter, too, and it's very difficult if not impossible to flush out any debris that might be lodged in it.
Since you're replacing and/or flushing everything, I would go with PAG oil...PAG-46 specifically.
User avatar
JohnHere
Posts: 294
Joined: Sun May 13, 2018 10:20 am
Location: South Carolina Upstate - USA

Re: Cannot get compressor to engage

Post by JohnHere »

Double End Capped PAG, if you can get it.
Beamer.619
Posts: 10
Joined: Mon Nov 16, 2020 4:18 pm

Re: Cannot get compressor to engage

Post by Beamer.619 »

my condenser is a old style condenser so it can be flushed easily I plan on using the same condenser. It looks like pag oil is my best option here since Im completely flushing the system out so I will be using pag 46 will report back when system is install and filled with refrigerant.
Post Reply