First time poster - and new owner of two( because one wasn't enough) '92 300D 2.5T's - great cars.

Anyway - I noticed over the weekend that while the AC controls were set to OFF in the cabin - the AC compressor hose (large fat one) was frosty white from condensation. Thinking this was odd - I turned the AC controls ON and the hose lost it's frost nearly immediately.

I have confirmed that the clutch is moving at all times regardless of the AC control settings in the cabin.

The car blows cold - and was converted to R-134 by the dealer back in '99.

This sounds to me like the compressor is on when it's supposed to be off and I would think this would lead to an early failure.

What do you guys think? What would cause this? Fault relay? Which one?

-John

Possibly the Klima relay (behind the battery) or the climate control push button unit (PBU). There are 2 switches on the dryer behind the left headlight. One has connectors on pigtails, the other has connectors right on the sensor. Pull one of the wires from the sensor - switch, actually - without pigtails. If the compressor disengages, the problem is with the PBU. If the compressor keeps running, the problem is with the Klima relay.

Sixto
87 300D^2

First unplug the compressor, if it still runs, then you need to re-align the clutch (spacers).

If it shuts off, then start tracing backwards.

__________________
Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2

I'd look at the Klima relay first. Remove the plastic splash shield behind the battery. My guess - the Klima relay has been removed and replaced with a wire jumper that runs the compressor all the time.

Excellent - thanks everyone. I'll confirm this weekend and post a follow-up.

Thanks everyone for the help so far. Here is what I have done any the results I found:

I replaced the Klima relay from my other '92 300D and had the same result (clutch engaged - AC running when controls set to off [the 0 button]). This other '92 300D operates as expected - the clutch does not turn unless AC controls are set to ON.

After the Klima relay had no change in the result I attempt to disconnect the sensor as mentioned above connected to the AC drier. With either connector off I had the same result - clutch continues to spin.

What does all this mean? BTW - I didn't see any odd wiring on the Klima relay. The only thing odd was that the relay was in a different connector/slot then the other 300D I own. Maybe due to the different options between the two cars?

Anyway - clutch continues to spin. Bad clutch?

-John

Does the compressor engage with no Klima relay installed?

Do what Eugene suggested - disconnect the wires atop the compressor. If the clutch remains engaged, the clutch is bad. If the clutch disengages, that's really odd and you'll have to trace the wire back to the Klima relay or run a new wire.

Sixto
87 300D^2