I have a 1991 300E. I just had the compressor replaced by MB. After three months of perfect performance, my CC is now acting pretty weird. Now and then I hear rapid clicking under the dash on the passenger side, then it stops after 5 seconds. I then notice that the CC fan (on high speed) runs for a bit, shuts off for five seconds, then comes back on slowly. The a/c is also not as cold as it should be, and it was cold!!

Would this relate to the fuse box in any way?

HELP!

Not sure how this all inter-relates. I am thinking maybe there is a loss of power to the system which is placing things in various emergency or backup modes, such as the aux fan running high, and as far as the temp, the AC may be doing what it should, but the heater valve (mono-water valve) is being activated, so it's throwing in some heat to the heater core when it shouldn't be doing that. A lack of power to the water valve (the failsafe mode, so to speak) actually applies heat, it takes power to shut off the heat, kind of logical when you think about it. So yes possibly it's fusebox related, I'd be more tempted to fault the pushbutton control panel though, rather common fault. Are you wanting to diagnose it yourself, or just asking for opinions or what?

Gilly

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I do want to diagnose myself...anyway to save $$ is good by me. This problem seemed to have started after I was checking fuses. Can fuses go bad, even when the visually look ok? Maybe this is all just a coincidence. But the fact remains...the CC just ain't right!

The fuse itself can't go bad per se, but the contacts can get corroded depending on locale which would increase the resistance and limit the flow of current. Sandpaper, emerycloth and D5 Cramolin from Caig are my suggestions. HTH-

Dave

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One thing to check is the sensor located overhead next to the light / sunroof. First try just vacuuming it off, making sure nothing is broken, etc. This can cause erratic fan speed, undercooled and overcooled air. Someone else here knows a way to test it.

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