Another type of AC problem
 

I have a 91 which I went back to a Holley and direct fire ignition. Everything works well except my AC and I would like to keep it. It has a fresh charge of R-12 and the compressor will blow very cold when shorted at the relay. I went through the manual today and did the troubleshooting - all of the components check out OK. I think I'm down to thinking the CPU is telling the AC to shut down because it senses other problems ( no EFI etc.)
Now the hard part - What do I do to work around the ECU and turn on the compressor? It also has to be cyclic so it doesn't freeze the expansion valve and blow the compressor. If indeed the ECU is at fault what type of signal is it sending? If it is a 12v signal can I disconnect a wire at the ECU? If it is an open circuit can I replace it with another keyed source? I know this is not the usual problem but I sure could use some help thinking this one out. Thanks in advance for any and all help.

Not much of a wiring guru on these cars, but if there is power at the a/c switch, go to a thermostat, with the probe on the evap, then on to the relay. The factory must have some type of unit that will detect freezeup, and cut the compressor out. Either a temp sensor on the evap, or a pressure sensor that will do the job. Maybe just go directly to that.

Back in the early 80's I purchased a '79 Limited that 1/2 the a/c had been removed because of problems. Long story short, I got it together, ice cold air, but after driving for 1/2 hours frost was coming out the vents. I put a thermostat on the evap and no more problems.

At least it will go back to the top.

Thanks - I know this is not the normal problem and that is the type information I am looking for. There must be other people who needed to do a similar thing. Let me here what you did to get it functioning corectly.