well this is better info to help you .. possible the ac pressure switch high pressure is bad saying the high side refrigerant pressure is too high , so fans come on and the ac compressor will not turn on..it overheated, boiled over because thermostat went bad. replaced it and that fixed the problem. now runs cool. driven over 500 miles since. but since replacing thermostat both the fans come on after start and stay on causing a/c not to turn on. replaced sensors and connector and wires, all relays and fuses.
the pcm pin C4-12 is the pin that goes to the high pressure switch on the ac compressor .bought used 1996 ss impala pcm and had flashed to stock specs. didn't change anything. only thing changed is 180 thermostat to 195, but don't think that would make a difference. going to change back to 180 tomorrow.