1994 E320 A/C blows cold when parked-ambient when driving-long
 

When I start the car and turn on the a/c it gets cold quickly and blows cold as long as I am parked. If I place the car in drive and proceed down the road, the air slowly warms back to ambient after a couple of minutes. If I stop the car, turn off the key and then start all over again the process repeats. It is pretty predictable in that I can get to a long traffic signal, turn off the ignition, and start it back up and enjoy a/c for the duration of the signal a a brief period after leaving the intersection.

I have tried other things to get it to reset but it seems nothing short of turning off the ignition will do it. Turning the a/c off and back on does not do it. Any other fiddling with the a/c controls is also ineffective.

I broke out my DTC "code reader" and got the following:
Pin 3 - 4
Pin 6 - 2, 4
Pin 7 - 1
Pin 8 - 1
Pin 14 - 5, 11

I cleared all codes and then tried to reproduce the problem in my driveway. I let the car sit in park for around 10 minutes and the compressor cycled as expected and the air was cold. I then placed the car in drive with the parking brake set and increased the rpm just slightly above idle. The car obviously did not move but the compressor stopped immediately (it has just started a few seconds bwfore) and did not start again for the next 5 minutes. I then place the car in park and turned off the ignition. After 10 seconds I restarted it and the compressor started again. I rechecked all the DTC pins and all are still clear.

The wiring harness was replaced over a year ago. And my belt used to slip but I just replaced it this weekend and no longer squeels. But the a/c problem has not gotten any better. Is my car possesed? Other that this is runs great.

Thanks in advance,
Dave

I suggest you use the search function, this is a common problem and has been discussed a million times before. Because there is so much in the archives, I'll give just two quick suggestions. 1) Measure the air gap on the compressor clutch. Use standard feeler guages for this, such as are used for adjusting valves or setting the gap on spark plugs. The clutch gap should be 0.50m. If it's at or above 0.70mm you'll start seeing enough slip to trigger the protection circuit. 2) Clean any oil/grease etc off the compressor clutch surfaces. Use brake cleaner, simple green, whatever works for you. This can eliminate enough slip that the a/c works normally.

- JimY

Actually I spent quite a bit of time searching but most of the results I found talked about compressors not being activated at all. Or belt slippage. I have not found any that talk about clutch slippage. I will see about checking that and do some more searching. Thanks for the response.

Dave

I had the same problem as you. After checking everything from clutch to the AC compresser relay and spending hundreds of dollars at MB dealership, the problem was still not fixed.

Finally, I found that 1 of the 3 wires going to the compresser was loose at the compresser end. Installed another connecter. AC has worked fine since.

Does this car have a compressor speed sensor? If so, I would check it first. A dirty speed sensor may work better at low speed than high speed, meaning that the system thinks that the compressor is slipping when it speeds up. Or perhaps it really is slipping.

If you have three wires to the compressor, you have a speed sensor. This was deleted from later models.

From no compressor to intermittent blower
 

Well I wanted to give an update on this problem. I checked the air gap which was ok. And I used brake cleaner on the clutch and no change. So I checked the connector and after close inspection found the center wire had only a single strand still connected. I broke the plastic part of the connector during removal so I bought a new one and then cut and resoldered all three wires. After reassembly, the problem is gone. Now the compressor will continue to cycle as normal even after driving for some time. Great right?

Now there is a new problem. After several days of no problems, now the blower motor has stopped working consistently. When I operate the controls I can hear the air doors moving and the compressor kicks in. But the blower fan stopped working. I thought it might be the blower but I wanted to check for codes before I posted again. So tonight I checked for codes and got the following:

Pin 3 - 4
Pin 6 - 2
Pin 7 - 1
Pin 8 - 1
Pin 14 - 1

Now here is the interesting part. After checking the codes I turned off the key and then started the car. Then I turned on the a/c and put the fan on high and the temp wheel on full cold and the fan started blowing like normal. After a few seconds it was blowing cold. I checked the compressor and it was working fine. After around 10 minutes I turned off the a/c and prepared to shut off the car. But just for fun I turned the air back on. No blower! Compressor kicked in, air doors moved but no fan. So now I know the blower is still ok when it wants to be. But it was only happy for one cycle after checking codes?

I have no idea what to try from here.