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Compressor noise at startup

ky90025 on Tue October 26, 2010 11:39 PM User is offline

Year: 1999
Make: BMW
Model: M3
Engine Size: 3.2L
Refrigerant Type: 134a
Ambient Temp: 77F
Pressure Low: 35-37psi
Pressure High: 150-160
Country of Origin: United States

Have a 99 E36 bmw m3 with a denso 10PA compressor. The ac compressor was making noise at ac startup (sort of a loud squealing/grinding noise). The compressor made no noise when it was running and cooled fine. Still I replaced the compressor with a new unit and put in a new dryer. I drained and measured the pag oil in the old compressor and put back the same amount into the new denso 10PA (used ND-8 which is guess is pag 46 double end cap).

Vacuumed the system for 1 hour and then refilled with 2.2 lbs of 134a (three 12oz cans of 134a).

I replaced the ac belt and tensioner and so I know its not a belt problem.

My new compressor often makes the same noise at ac startup (especially if I turn off the ac then turn it on again after waiting 1 min) quiet once it is running. One experiment that I did was run the ac for 5 min then turn the engine off. After about 1 minute I tried turning the ac compressor by hand and felt a lot of resistance (turned the center portion not the outer pulley). Is this normal?

My other car an audi with a denso 7SB has very little resistance and turns easily by hand.

My low and high pressure is 33-35psi and 150-160 psi at idle at 77F which seems pretty normal. It cools ok. Car has 76k miles and the refrigerant oil seemed clean when I opened it up to replace the compressor. This car is driven about twice a month. Could the expansion valve cause this problem with noise at startup? I know I added the right amount of r134a but could too much oil cause this?

R-134a put in 2.2 lbs
ND-8 PAG 46 total capacity 120 ml (added what drained (about 1.5 oz) from old compressor plus 1 oz for dryer ) has 2 oz oil added from previous vacuum and refill

What can be causing this noise from the compressor at ac startup? Why is the compressor have so much resistance to turn in the beginning. If I turn if by hand for a while it will eventually turn easier.

After reading a lot of posts on the web I am think that my compressor is slugging liquid 134a. Could a bad expansion valve cause slugging? My ac does blow cold air, about 50F in the center vent with 80F outside air.

Thanks in advance.

Edited: Wed October 27, 2010 at 7:33 PM by ky90025

Chick on Wed October 27, 2010 5:34 PM User is offlineView users profile

"noise from compressor at startup"..Are you saying that when the car starts, and compressor is off, or "ONLY" when the compressor is on...kinda hard figuring out what you mean..
If you mean the car is making noise and you feel it's the compressor, might be another pulley on or off that drive, like a water pump, or the other belt/tensioner??

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Chick
Email: Chick

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ky90025 on Wed October 27, 2010 7:32 PM User is offline

Quote
Originally posted by: Chick
"noise from compressor at startup"..Are you saying that when the car starts, and compressor is off, or "ONLY" when the compressor is on...kinda hard figuring out what you mean..

If you mean the car is making noise and you feel it's the compressor, might be another pulley on or off that drive, like a water pump, or the other belt/tensioner??

Not when the car is started. When the ac is switched on. The noise is also present if I start the car with the ac on (ac not turned off when car was shut off).

Dougflas on Wed October 27, 2010 8:50 PM User is offline

May be liquid refrigerant migrating into the compressor during equaliztion period. Gm had that very problem. The fix if my memory is intact was repositioning of the hoses.

JACK ADAMS on Thu October 28, 2010 12:05 PM User is offline

This is called “Liquid Slug” at start up. I think GMtech can verify this. I have a full size GM Blazer that will do the same thing only in the winter times. If I park in a declined drive over night and start the a/c it will sound like the compressor is going to lock up for about 2seconds and then goes away. I can never get mine to duplicate till the next day. This may not be the case with yours but sound very familiar.

You will have resistance in the compressor after shut down till it is fully equalized, this is normal.

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