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Old 07-12-2003, 12:48 PM
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Join Date: Mar 2002
Location: Naperville, Illinois
Posts: 92
Another A/c Problem!

I'm trying to sort our the A/C system in my son's 88 190E 2.3. Replacing the condenser took car of the leaks. The system now holds pressure. While at it, I installed the fittings to convert the system to 134. Now, the problem starts. When you activate the A/C, the compressor clutch will kick in and the system cools very nicely............for about a minute! Then the compressor clutch disengages. Since the system cools and there are no unusual noises from the compressor, I am assuming that the compressor is fine. But, whatever controls the clutch is de-energizing it.

I have tried jumping across the low pressure cutout switch installed on the dryer, but that makes no difference in operation.

Can someone provide me with information on the items that control the A/C clutch on this car, and WHERE each item is located. I know that there has to be a hidden sensor somewhere that I am overlooking!

If I could understand the systems that control the clutch and knew where the components were located, I should be able to fix the thing! Unfortunately, the Haynes manual is totally lacking when it comes to A/C systems.

Thanks in advance.
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Old 07-12-2003, 01:14 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
There has top be a thousand posts on this topic just this year. I'll give you some brief details of what you should look for and then use the archives to read up on which area looks promising.

the system has basically two controllers in series so to speak. The pushbutton controller decides on whether or not to turn the compressor on based upon its inputs.

The compressor on signal should be conducted to the klima relay (compressor control relay) through the low pressure switch. This wiring is real easy to view and is the first step in your diagnosis.

In most cases the signal from PBC to Klima is a ground but sometimes its 12v monitor the signal as you turn the A/C on to verify condition of the signal and whether it goes away when the problem exists.

It will probably stay as your systems indicate to me that the Klima relay is stopping the compressor. It does it to protect the engine and compressor from various mechanical problems. It protects the engine from overheating by shuting down the comp. It protects the belt from a frozen compressor by monitoring the engine and comp speed. In this function comes much of the problem. Loose/slipping belts, slipping clutches due to various oils on the surface, etc etc,

And then the last thing you should look for is the logic and plan to lobotomize the Klima when all else fails.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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