86 300E Fuse #7 problem
 

Car has 89K miles and has experienced no problems with the A/C in the 1 year I've owned it. It has a somewhat 'goofy' control unit (auto fan is always high, erractic temp changes) which I will need to replace at some juncture.

The A/C was blowing ice cold when the entire unit went dead and started blowing HOT air. #7 fuse was blown, so I replaced it (several times) and I can run the control unit as long as I don't engage the compressor (economy / vent mode). It will run for a couple of seconds and blow the fuse again.

What are the troubleshooting steps?