Not sure about the voltage drop. But I was wondering if the pcm has anything to do with it. I know on my Jeep, I had a short on a ground in the pcm that wouldn't let the ac compressor come on, till I changed out the pcm. But you have given me an idea. I will pull my glove box and see when it is not blowing out the vents and see if it is blowing out the circulation door.

 

interesting, on the PMC, I bought this truck from a guy that had the PMC rebuilt, I am thinking mine is less than a year old. you might be on to something, if it is a bad ground the volts could drop or not have enough voltage to hold a gate or actuator in place. My AC was really low on Freon, when I added to it, it worked longer, but no fix, how is your Freon?

 

It is good. I have had it apart twice and had to put new freon in it both times.