I had our a/c overhauled this March with a new compressor and refilled with Freeze12 on 1992 745. I have been very happy with the results so far, blew very cold up until yesterday. We had driven about 45 miles with cold air, then turned off the car and went into a mall. When we came back out it was raining so turned on the defrost. Once the windows cleared turned the (manual) switch back to dash vents. Air was no longer cold, just outside temp air. Stopped by my mechanic who did the a/c work and as would figure he is out on vacation until next week. There was no visible evidence of having lost any of the coolant. I checked the fuses under the ash tray and have not found any blown. The car is not overheating. I checked the FAQ but have not found a similar problem. Any ideas where to look next?

Yes these boxes fail and frequently. They are called climate control units. The one in my '92 is manual(has dials) like yours, as opposed to newer models that have a temp setting in degrees.
Mine failed all of a sudden like yours. I removed the unit and I looked for broken solder or brown spots on the circuit board, and resolder the spots. It did not work in my case. Other bricksters have had success with the resolder.
I bought a used one for $200 and system works fine. This is a $600+ part at the dealer.
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John '88 240, '92 740 Tampa Bay

The A/C control panel on these cars is known to fail unexpectedly (the box with the dials for fan speed, temp, etc) such that you cannot turn the A/C on. I have not had this problem myself, but others on this board have reported a faulty solder joint somewhere inside the box that may need to be repaired.

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Matt L. -- Cary, NC -- '89 740 sedan -- '91 740 wagon

After reading the FAQ I considered this, but the posts in the FAQ talk about "climate control" panel. I assumed this is a electronic automatic climate control unit i.e. you set a temperature, not a manual panel where you turn a dial. Mine is manual dials. Does the panel circuit board problem apply to a manual dial setup?

Also did not mention in initial post, the compressor is not cycling on/off. So I figure it is something electrical.

My understanding is that the automatic climate control box is even more flaky than that manual dial box that you have, but even the manual box has been known to fail. They come up on e-bay all the time if that tells you anything. I think someone had this problem very recently (in the last week or 2) and resolved it by resoldering a joint inside the box. Scroll down and find that post or maybe that person will post here and give us the details.

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Matt L. -- Cary, NC -- '89 740 sedan -- '91 740 wagon