My '89 300SEL's air conditioning stopped working. The compressor is not engaging at all. I also noticed that the aux. fan is not running (even at high engine temps). I don't know if the two things are related. In the cabin, the vents are getting airflow, as if the system is trying to work, but they are blowing warm air (doesn't seem to be heated, just ambient air temperature). Fuses all seem to be fine.

I don't have R12 equipment, so I want to rule our electrical trouble before moving on to coolant.

What would be a reasonable list of things to check to rule out (or find) electrical troubles with the A/C system?

Thanks.
-Brett