I am still digging. I talked to Rick Vyncke about his problem. He discovered the next time he used his fan/heat/ac head unit that it worked. But after running his air conditioning for 20 minutes or so it would kick out for a while and turn on again. My guess is he has something going on with the air conditioning devices where they are pulling too much power and overheating the thermal breaker in the power bay. My problem is different, at least, the symptoms are different.
I checked the six wires going into an 8-pin Delphi connector behind the dash leading to the back of the fan speed knob. One wire is hot, 13.6v. I checked the same lead coming out of the Delphi connector before and after it splits - 13.6v on both wires after the split. This is all with the fan speed knob in the off position. Immediately when I turn on the fan speed knob the hot wire loses power. How can that be?
The dash fan/heat/ac head that sits in the dash is readily available on the internet, part number 16233143, and is a commonly used GM part from the late 1990s to early 2000s. The part cost is from $130 to $185. But as Mr. Farris continuously states, paraphrasing - "Don't throw parts at the problem. That can get expensive. Properly diagnose the problem and replace only the part/s that is/are bad."
What is the next step to diagnose this problem?