My 1989 300E has an a/c problem! When driving the car I turned on the cool air and it was working fine for about 20 min then suddenly very hot air started to come out of the vents. I turned the air off and turned it on again and the hot air was still there. I went home and turned the car off. About 3 hours later I took the car for a drive and the cool air was back. 20 min later hot air again. What could be causing this problem? I changed the push button controls for the heat and the a/c system on the dash and I cleaned out the small sensor on the roof where the sunroof controls are. All out of ideas.

Please Help

Fab

Belt slippage is the most common problem...system monitors the engine speed VS the compressor speed..IF the compressor SEEMS slower the "KLIMA" relay shuts the compressor off until you re-start.

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Thanks for the reply but how do I check for belt slipage. I replaced the serp belt 2 months ago and found out that the 13mm bolt that rasies and lowers the tensioner is not working. The bolt just turns in its spot and nothing happens. I had to force the belt on (do not ask how), but this air conditioning problem has been happening for about a year now. When I checked the belt it seems pretty tight.

Thanks

When hot air starts to come out, is the compressor still running?

I was doing some research on my problem and came across this. There's a tsb for the "Evaporator Temperature Sensor/Switch" that sounds similar to your problem, but mine is on a 1999 C230.

AF83.30-U-6000A

The description they give is:

The A/C system will run for approx. 10 minutes, then the A/C compressor will switch off, and will then run again for 10 minutes after ignition is again switched on.

Maybe it's a similar thing? Good luck,
Don

I have a 88 2.3 190e,where is that sensor located? because mine does the same thing but only comes on for about 5sec.
Also, curious about how to clean out your compressor & if theres any specail tools to do so?