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Old 02-13-2011, 08:48 AM
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W124 Climate Control Issues

Greetings,

I just got a '93 300E 2.8 for a song. It's in great shape (just a couple of minor fixes) except for the climate control. I get no response when pushing any of the buttons or turning the temp control. The blower come on and the compressor doesn't kick in.
1. How do I begin troubleshooting the system?
2. Where can I find a FSM?
3. Barring that, is there any service manual available?

This is my first Mercedes and I could use any help at all.

Bob

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Old 02-13-2011, 03:44 PM
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Start out by checking fuses, sometimes they are blown and sometimes they are not making good contact. Also there is a separate strip fuse in a black plastic holder bolted to the driver's side strut tower top.
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Old 02-14-2011, 09:26 AM
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Welcome,
Since the BLOWER works, most likely issue isn't a fuse.

The compressor is controlled by a compressor (KLIMA) relay.
That relay gets signals from a/c pushbutton & sends command signal to the klima relay.
That relay gets RPM signal & refrigerant fill message & then turns on the compressor.

How good are you volt meter skills?
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Old 02-14-2011, 11:12 AM
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There is a detailed troubleshooting flowchart in the climate manual. It specifies use of a special tool for checking the climate system. The tests can be run using a simple DVM, if you are willing and able to simultaneously read the wiring diagram. It's a lot of work.

You haven't specified whether you are trying to heat or cool the cabin - it makes a difference. Since you're using USA model nomenclature, I'll assume the former. Try the simple test in the following paragraph.

A simple place to start - try unplugging the auxiliary electric water pump. It is located (I think...varies a bit on different 124 models) in front of the battery, with the monovalve. There is a connector on the pigtail that can be undone. The pump tends to short out after a dozen or so years, which causes the climate control pushbutton unit to go into a protection mode that more or less is what you've described.
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Old 02-14-2011, 11:57 AM
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Quote:
Originally Posted by mbdoc View Post
Welcome,
Since the BLOWER works, most likely issue isn't a fuse
I'm not sure since the post says he gets no response from pushing buttons, but also says "the blower work"? Figured I'd cover the strip fuse also.

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