Cannot get compressor to engage

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

Moderators: bohica2xo, Tim, Dougflas, JohnHere

Beamer.619
Posts: 10
Read the full article
Joined: Mon Nov 16, 2020 4:18 pm

Cannot get compressor to engage

Post by Beamer.619 »

Just recently put new oil into my compressor since there was a leak in my ac system, I fixed the leak and also replaced the drier but when I fill the system up with refrigerant and the car is running with the fans on max with the ac on I cannot get the compressor to engage. I filled the lowside with 75 psi of refrigerant until the system wouldn't accept anymore refrigerant and the clutch tried to activate for a second and then gave up and after that I couldn't get the clutch to engage at all. So I thought my compressor clutch was bad so I got the clutch to engage by supplying power from the cars battery and the clutch was engaging in and out while the car is off. I then checked the resistance and it was reading .2 ohms which is obviously not in the 2 to 5 range that people say I have also check the connector wire going to the compressor and it was getting power. Does anyone know why my compressor wont engage and why are my ohms reading are so low but the clutch still engages when suppled manually with power?
Dougflas
Posts: 366
Joined: Mon Apr 18, 2016 6:10 pm

Re: Cannot get compressor to engage

Post by Dougflas »

Make and model of vehicle would be a huge help
User avatar
JohnHere
Posts: 359
Joined: Sun May 13, 2018 10:20 am
Location: South Carolina Upstate - USA

Re: Cannot get compressor to engage

Post by JohnHere »

The only way to correctly charge a system is by weight, not pressure, using the appropriate tools and equipment. Please post the make, model, engine size, and year of your vehicle and we'll be able to tell you what the charge weight and oil amount should be if it's a USA-spec vehicle.
Beamer.619
Posts: 10
Joined: Mon Nov 16, 2020 4:18 pm

Re: Cannot get compressor to engage

Post by Beamer.619 »

Its a Bmw 750il 1992 e32 series I also drained and refilled the compressor recently when i fixed the ac leak with 5.7oz of ester oil because the car was converted from r-12 to 134-a in 2000 and its says they used ester oil on the retrofit tag.
Beamer.619
Posts: 10
Joined: Mon Nov 16, 2020 4:18 pm

Re: Cannot get compressor to engage

Post by Beamer.619 »

https://imgur.com/a/bqqS4rv
There's a picture of the compressor info I couldn't find any info online about it.
Also the compressor was running while there was a leak and it was making the air cooler but since it had a leak I don't think it was working very affective.
User avatar
JohnHere
Posts: 359
Joined: Sun May 13, 2018 10:20 am
Location: South Carolina Upstate - USA

Re: Cannot get compressor to engage

Post by JohnHere »

Interestingly, in my references, there are no refrigerant and oil specs listed for a 1992 BMW 750iL e32, only for 1989-91 and then from 1993-94, suggesting that BMW wants us to go by the under-hood decal.

That being said, the actual clutch resistance of only 0.2 ohms indicates almost a dead short in the windings. Since your car is around 28 years old, the wiring to the compressor is probably compromised somewhat by age and corrosion such that full battery voltage isn't reaching the coil anymore. Connecting a jumper from the battery directly to the compressor terminal does provide full battery voltage to the coil, which probably is enough to activate the clutch even in its compromised state.

I would replace the clutch assembly, then recover, evacuate, and recharge the system to about 80 percent of the R-12 amount. Unless the under-hood decal is still visible, the best I can do from here is to provide the specs for the 1989-91 models, all engines, with rear A/C: 73.0 ounces of R-12 and 10.0 ounces of mineral oil.

Lacking an under-hood decal and guessing that these specs are the same for your 1992 model, an 80 percent charge of R-134a would be about 58 ounces.

The total amount of oil that's in the system now can only be guessed at as well. However, you said that you replaced 5.7 ounces of ester oil in the compressor with the identical type and amount of oil when you repaired the leak. And since the system ran okay since its conversion to R-134a without the compressor seizing up, we'll have to assume that the oil amount is currently about right.
Beamer.619
Posts: 10
Joined: Mon Nov 16, 2020 4:18 pm

Re: Cannot get compressor to engage

Post by Beamer.619 »

Here's a picture of the retrofit tag https://imgur.com/e5BGFDS It says they used 4.24 lbs of refrigerant idk if they meant to write it in the oz's line because that would make more sense because 4 pounds sounds like way to much. And for the oil type I'm pretty sure they wrote ESTERCOOL which is ester oil with and additive I just refilled it with regular ester oil with a UV dye in it because I was trying to get this project done. It says they used 4 oz for the oil the reason I put in 5.7 was because I replaced the drier and that takes about 1 oz and I also flushed the condenser so I thought the extra .7 would not hurt.
Dougflas
Posts: 366
Joined: Mon Apr 18, 2016 6:10 pm

Re: Cannot get compressor to engage

Post by Dougflas »

The way I read that is 4 lbs.24 oz so it's 4 1/4 lbs.
Beamer.619
Posts: 10
Joined: Mon Nov 16, 2020 4:18 pm

Re: Cannot get compressor to engage

Post by Beamer.619 »

yikes so I just looked at the bottom of the compressor and realized that there is still a leak in the ac system coming from the high side line that connects to the compressor (no this is not the original leak this is a different one) I was confused why it was leaking from this line because I replaced the o-rings on both lines before I installed the compressor last time, I then realized there looks to be a chip on the line of the high side hardline right next to where the hardline connects to the compressor. Here a picture of the chip on the hardline I circled the chip in red https://imgur.com/khSe1cG . Could this be the reason of the leak I'm guessing it is because there was ac oil sitting right underneath the line where the chip is you cant see the oil in the photo because I wiped it down before I took the picture. The reason I thought the system was sealed was because it was holding pressure so I'm guessing this is a slow leak.
Beamer.619
Posts: 10
Joined: Mon Nov 16, 2020 4:18 pm

Re: Cannot get compressor to engage

Post by Beamer.619 »

UPDATE: I uninstalled the compressor once again from the car an tested the resistance and I got it to read 4 ohms the reason I couldn't get it to read that before is because I was touching the multimeter probes in the wrong location, Its a older style compressor it has more wires than a newer compressor. So my only guess of why the system isn't running is properly is because of the chipped line going from the compressor to the evaporator that was causing a slow leak. Anyone think it could be something else?
Post Reply