Hi M.B. Doc;

Thanks for your response. In answer to your question as to what is the problem, I've copied and pasted the pertinant facts from a previous post of mine entitled "AC Help 2 Years in a Row".

1) Yesterday, after leaving my 1991 300E parked all day, the AC never came on upon starting. It had worked fine up until yesterday morning. Now this happened intermittently last year and just as I was at the end of my rope, it started working again and has been for the last 7 months-until yesterday.
Last year, if I would hit the AC off button and then turn it on, I would sometimes hear the vents operate (sounds like it opens or shuts) and the AC would work along with the air recirculating switch. Sometimes back then, as it is doing now, the AC switches don't do anything, the air recirculating switch is doing nothing, and hot air blows out the windshield defroster vents and I can't turn it off.

2) OK, here's a new twist!

After not working for almost 2 weeks and me trying everything to make it work, the AC just started up this morning, the air recirculating button worked, and everything was good with the world again.
For 5 minutes! then it cut off again.
Stopped for a cup of coffee at 7-11, got into the car, and lo and behold it was working again for the ride into work.
So fuses are intact, compressor is working, I'm assuming all the vaccum lines are fine, etc.

Any ideas?

3) In a continuation from the above post:

Parked the car a work for 3 hours (in the sun, if that has any bearing on anything) with the AC system working prior to working.
Got into the car to do errands and the AC was not working again.
Parked the car for approx. 2 hours (in the sun) and upon startup, the AC works again.

Help!

P.S. I went ahead and bought a climate control unit from eBay this morning