Is It the Compressor? - PeachParts Mercedes-Benz Forum

Tom Evans · #1 04-26-2009, 04:34 PM

Year: 1981
Make: Mercedes
Model: 300SD
Engine Size: 3.0L
Refrigerant Type: R12
Ambient Temp: 79degF
Pressure Low: 60
Pressure High: 125

I just replaced my R4 compressor with a new (not a rebuilt) Compressorworks compressor, along with the receiver-dryer. I have thoroughly flushed the entire system twice. I also carefully added oil throughout the entire system, including 90 Ml in the compressor. I turned the compressor over by hand for 40 revolutions. The system held a good vacuum overnight. Total evacuation time was 4 hours.

When I started adding R12, I noticed that the low side was not going down as I would have expected and the high side did go up as high as expected. There was some cooling, about 5 degrees differential from ambient. One other thing I noticed was that both needles on my gauges were fluttering, something I haven't noticed before.

Which brings me to the title of this post: Is it a faulty compressor? Did I do anything wrong in the installation? I have installed about 8-10 R4s and this is the first one that acted this way.

Thanks for your help.

leathermang · #2 04-26-2009, 05:37 PM

Was the car at high idle...
and did you have a fan blowing across the condenser ?
Were you installing vapor and into the low side valve ?
Are you sure your compressor engaged ?
Did you jump the pressure switch to get it to engage or did it due to pressure getting high enough ?
Did you have the inside temp control set to max and the high blower on ?

tangofox007 · #3 04-26-2009, 08:08 PM

Quote:

Originally Posted by leathermang

Did you have the inside temp control set to max...?

Let's hope not!!!

leathermang · #4 04-26-2009, 11:21 PM

Quote:

Originally Posted by tangofox007

Let's hope not!!!

Max cool you silly wabbit.

Tom Evans · #5 04-26-2009, 08:56 PM

Quote:

Originally Posted by leathermang

Was the car at high idle...
and did you have a fan blowing across the condenser ?
Were you installing vapor and into the low side valve ?
Are you sure your compressor engaged ?
Did you jump the pressure switch to get it to engage or did it due to pressure getting high enough ?
Did you have the inside temp control set to max and the high blower on ?

Engine was at 2,000 RPM.
I start charging vapor through both the high and low sides WITHOUT the engine running. Then I close off the high side and crank the engine and finish charging through the low side as vapor.
Compressor is difinitely engaged.
I did not have to jump the pressure switch.
The temp was set to max cool and the blower was manually set on speed 6.
No fan on the condenser. It was 79 degrees ambient.

Matt L · #6 04-26-2009, 09:23 PM

High low side pressure with fluctuations can be caused by bad or sticky valves.

leathermang · #7 04-26-2009, 11:24 PM

The combo of not high enough, not low enough and fluctuations sure does sound like a compressor problem.

Tom Evans · #8 04-27-2009, 11:30 PM

I replaced the suspect compressor tonight with a known-good used compressor. That was the problem. As soon as the compressor clutch kicked in, the low pressure went down and the high pressure went up to the expected values with steady gauge readings. I figure that the suspect compressor had one or more bad reed valves.

JimmyL · #9 04-27-2009, 11:42 PM

Good find. I hope you were able to reclaim the R12 you had charged the system with........
Sure does throw a wrench into things when your NEW part is defective!

Cr from Texas · #10 04-27-2009, 11:56 PM

Quote:

Originally Posted by Tom Evans

I replaced the suspect compressor tonight with a known-good used compressor. That was the problem. As soon as the compressor clutch kicked in, the low pressure went down and the high pressure went up to the expected values with steady gauge readings. I figure that the suspect compressor had one or more bad reed valves.

You just ruined my plans for the weekend.
I was planning to get a new "Compressor Works" R4, new drier, and new expansion valve (that would give me a 2 year warranty buying all three from Autozone).

Any one else have a bad experience with the Compressor Works brand?

JimmyL · #11 04-28-2009, 12:00 AM

Quote:

Originally Posted by Cr from Texas

You just ruined my plans for the weekend.
I was planning to get a new "Compressor Works" R4, new drier, and new expansion valve (that would give me a 2 year warranty buying all three from Autozone).

Any one else have a bad experience with the Compressor Works brand?

I must say, the largest purchase I have made from Fastlane was a rebuilt R4 compressor and that thing has been as good as I could have hoped. I think I'm entering either my 3rd or 4th summer with it.
Haven't experienced the fine work of the Compressor Works brand. More like Compressor Don't-Work......

leathermang · #12 04-27-2009, 11:46 PM

Good, now Jimmy... go back to Pizzachef's thread....

leathermang · #13 04-28-2009, 12:06 AM

Cr, it may be that some have not specified the correct R4 for the refrigerant they were using...
Check with Tray at Carlisle Auto Air in San Antonio to make sure you are on the right side of the design curve...I think I have posted the correct later serial numbers...
Particularly if you are using R134a...

vstech · #14 04-28-2009, 08:57 AM

just a note. you mention replacing the compressor, the dryer, and the oil.
what about the expansion valve?

Tom Evans · #15 04-28-2009, 01:22 PM

I've had good luck with Compressor Works in the past. I have one on my other MB. It has worked well since 2004. That's why I wanted another Compressor Works unit. That and the fact that it was $70 less than a new Delphi. We'll see how AutoZone handles it.

Yes, I do recover R12. I wouldn't be working with R12 if I couldn't recover it.

My concern now is whether I need to flush the system out again. The oil I drained out of the defective ceompressor was darker in color than it went in, but there was no particulate matter in the oil. Also, should I change out the receiver/drier? (It was replaced along with the Compressor Works compressor)