Have you had any luck fixing this problem? I have what appears to be an identical problem. 1992 Olds 88 w/ auto temp controller. Fan speed control started acting up (wouldn't come on, then couldn't control), next temperature display on in-dash A/C & heater control module started flashing, then A/C quit.
Had system pressure tested and everything is good. Applying voltage to compressor engages clutch & a/c works fine. Shop diagnosed and thought it was likely a faulty auto temp controller. I'm told it's located on the firewall on the RH side of the passenger compartment but I haven't had time to look yet. These units are pricey, so I didn't just want to throw money at it without checking things further. I feel it could also be the heater & a/c control module (even more expensive).
Anyone have access to a wiring diagram for the A/C system they are willing to share? I've got a couple of long trips coming up and need to fix this ASAP or i'm going to melt. I'm at the point of hardwiring a switch to engage & disengage the compressor just to get by until I find the problem. I don't like this solution, but I'm getting desperate.
Any help would be appreciated!