2nd Gen Non-Engine/Transmission AC problem on my'97

[coadman]

Just noticed this the past few days, when I tried running the AC. AC works when I start out with fan on about the 3rd high notch or lower, and the coolant knob about 1/3 of the way towards the coldest spot. If I try to move the coolant knob to the coldest position, I immediately get HOT air coming our the vents, and it doesnt matter if I move the knob back towards less cool, it still blows hot air. This also happend to me once, when I switched the fan up on high. Sometimes, if I shut the truck off for awhile, say 15 min or longer, and start back up, the AC works as normal, as long as I dont have it on too cool or the fan on too high. Anybody have any ideas what I may look for?

thanks,

coadman