Symptoms: Each summer my 126 (1986 300 SDL) gives me a few weeks of cold air and then gradually diminishes. It will get warm either while I am driving or when I start up. If I turn the car off and start up again it will get cool again. this happens more and more as the summer goes on until it works very infrequently. Last summer I replaced the klima relay with a used one that had a 1 yr. guarantee. It did make the AC go out less often but didnt solve the problem. This summer I replaced it and it worked well a few days but is doing the same thing.
PROPOSED SOLUTIONS: Independent mechanic gives me a different answer everytime I talk to him. First he recommended fixing the vacuum but he agreed it might not fix the problem and all it addresses is getting the air to flow out of the correct vents (I get cold air out of the window defroster vents and sometimes warm air in a front vent to the left of the steering wheel when the other vents are cold). So when the ac acted up again I brought it in and he said the klima is not the problem or it would never blow cold air. He again said to fix the vacuum (the last time he quoted 1600 but this time said it "shouldnt be that much"). He called me at the end of the day and instead of giving a quote for the vacuum system he said he replaced the klima relay since it was still under warranty. Worked great a few days and now blowing inconsistent again. Anyone have a suggestion as to what to try next? Get another relay? Fix the vacuum system? As you can tell I am clueless about how to proceed.

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86 300SDL

The KLIMA relay will disengage the compressor if it detects a speed difference between the engine and the a/c compressor. This is designed to prevent the belt from being damaged in the event of an a/c compressor lock up.

Sometimes if the KLIMA relay has internal problems it can kick off and shut down the compressor.

One way to test and see if the KLIMA is the problem is to bypass it with a standard relay. This takes some work but can be done.

Another issue you might be seeing is a faulty evaporator temperature sensor. If the sensor is bad it could be prematurely shutting down the a/c compressor.

Sorting out the vacuum system is a must though. If you dont have all the pods working well then you wont get air in the right places.

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thanks for the suggestions! Is the temperature sensor easy to access? What does it look like and where do I find it? Thanks in advance.

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86 300SDL

I had a bad evaporator temperature sensor in my 240D. It could be remedied by turning a POT.

In the w123 case you could access it from under the glove box. In the w201 it is by the blower motor under the windshield wiper. Not sure where it would be in your car.