A/C Compressor Issue

[jshz2003]

I've got a '90 325I convertible. The A/C hasn't worked since I got it back in March. When I press the A/C switch I hear it kick in and the engine accelerates. Watching the compressor, I can hear the clutch kick in and the center part starts to turn but ratchets and eventually stops rotating around except every once in awhile it'll turn a bit. I but a gage on the system and the pressure reads about 45PSI (it was already converted to 134 when I bought it). I've checked the pressure a few times and it is always at PSI with the A/C on high. Do I need to go and have the whole system evacuated and try re servicing it or is the compressor shot?

[romeomike]

I have a '90 325iC as well, with the same issues, except at one time it did work. The (independent) service tech put in 1.5 lbs of refrigerant, and when he applied power directly to the compressor clutch, things worked. He laid off the next troubleshooting steps, which would have involved pulling the center console.

Over the next couple of days, I plan to do that...

Once that's removed, on the driver side are the evaporator temperature regulator (a six terminal device that looks like a large relay) and an evaporator temperature sensor. The Electrical Troubleshooting Manual has a series of procedures to check those two items, wiring at the evaporator temperature regulator, and the AC select switch. The advantage of all this is if you find problems here, you don't have to evacuate the system to repair them.

I'll post what I find.

I know the aux fan (the one just behind the grille) turns when the AC switch is depressed (good), and the idle speed goes up (so the ECU is OK). So the only two failure points that would require evacuating the system would seem to be the pressure switch or the compressor.

Praying for a cheap fix....

[silversled]

Here's my take, I have an 88 325iC and the air conditioner has expired. I don't like A/C anyway so I have cut the fan belt to the compressor but nothing else...the A/C is all there....anybody who would like a free part is welcome...

[romeomike]

Originally Posted by silversled

Here's my take, I have an 88 325iC and the air conditioner has expired. I don't like A/C anyway so I have cut the fan belt to the compressor but nothing else...the A/C is all there....anybody who would like a free part is welcome...

I don't know if I'll need that just yet, but it's a kind offer all the same.

Now for the recap of today's troubleshooting:

Rule 1 -- check to see if there's any pressure in the system before you do anything else. I did that at the back end (oops).

I pulled the consoles to get the necessary access, and as a sidebar, installed a 2721 bulb into the red check engine light spot on the instrument panel without having to pull the instrument panel -- just enough room with a long set of needlenose pliers. Did the five-pedal-stomp test and the ECU checked out OK, as I now could see the flashes of the check engine light.

The Evaporator Temperature Regulator (ETR) passed all the tests except continuity between terminals 2 and 5. That's the circuit involving the refrigerant pressure switch (RPS) attached to the receiver/dryer.

Mercifully, I had continuity through the wiring harness from the ETR up the point where the RPS plugs into the harness (= no wire breaks to find or bypass).

I created a bypass for the RPS, but still no cooling.

Finally I attached a pressure gauge to the low and high sides, and had 0 psi on both. By comparison, I had 15 psi on the low side of my 91 318i. I'll get to have a friendly chat with the garage about "losing" 1.5 pounds of refrigerant they put in two weeks back while they were doing other things with the car.

Well, that's all the fun I can stand for now....

[romeomike]

Had the AC pressure tested for leaks -- passed. Changed fittings for R134, evacuated the system for 15 minutes, then they put in 1.8 lbs of refrigerant and the requisite amount of oil. So far, so good.

Off to the salvage yard to look for more E30 parts....

[mtccl]

Originally Posted by romeomike

Had the AC pressure tested for leaks -- passed. Changed fittings for R134, evacuated the system for 15 minutes, then they put in 1.8 lbs of refrigerant and the requisite amount of oil. So far, so good.

Off to the salvage yard to look for more E30 parts....

You should be good if you pulled a good vacuum on the system. This is where people fail. They don't pull a good vacuum, leave moisture in the system and the moisture kills the compressor.

Your process sounds OK. Have saved many compressors over the years doing the same.

[romeomike]

Originally Posted by mtccl

You should be good if you pulled a good vacuum on the system. This is where people fail. They don't pull a good vacuum, leave moisture in the system and the moisture kills the compressor.

Your process sounds OK. Have saved many compressors over the years doing the same.

Thanks for the encouraging words, especially as another Vegas summer will get here soon enough.

[mtccl]

Originally Posted by romeomike

Thanks for the encouraging words, especially as another Vegas summer will get here soon enough.

Only thing I forgot to mention is I always change the evaporator dryer. Especially if the system sat "open" and/or uncharged. Imagine the entire time the dryer would be trying to dry continuously moist air and would be shot.

If the system was just low on charge and not "open" then you should be OK. If it loses pressure over the next couple of weeks; thereby confirming you have a leak somewhere (normally an o-ring at a fitting) , fix the leak and before repeating the above procedure I recommend you replace the dryer/evaporator also. Otherwise you should be OK. My daughters 94 Altima had 170,000 on it 2 years ago when I bought it and I did the above (& replaced dryer) and it has had A/C ever since and now has 215,000 on i the ODO.

Did the same on my 21 year old Porsche 944 and it has ice cold A/C for 3+ years also.

Good Luck!!

MM

[romeomike]

I'll keep an eye on it. Mercifully, the receiver/drier for the 90 is a relatively cheap part (in the $20 range) IIRC.