I'm having my 92 190E 2.6 A/C serviced and the mechanic is stumped. He said it's a problem he hasn't seen before, so I'd thought I'd post it here to see if I can find an answer.

It all started with a seized compressor. It turns out the compressor was hot wired to be on all the time and bypass the push button control. My mechanic replaced the compressor, clutch, drier, and expansion valve and flushed the system for a few days. The A/C works nice and cold with the hot wire to the compressor. But we can't leave it that way since it led us to this problem in the first place. (I don't know what this hot wire is doing, except it seems to bypass any attept to turn the compressor off in the climate control system).

He removed the hot wire and installed a new push control unit since the current one is fried. Within minutes, the new control unit fried. That's pretty much where it stands. The mechanic is trouble shooting a few things, but hasn't found out exactly what is causing this problem. He mentioned a possible aux fan in the heating system as the culprit but has now ruled that out. Right now, he also mentioned some potentiometer that's burried deep within the dash that could be causing the problem.

Any idea what could be causing a short in the system? Or why someone would even hot wire the compressor in the first place?

Thanks!