What causes cooling fans to come on too early?

[dhutton]

Originally Posted by 72Z/28

I have OEM ECU with blue and red connectors. Dark green wire (pin 42) and Dark Blue wire (pin 33). Both going from ECU or PCM to fan relays.

Both fans come on as soon as turn on the AC even with cold engine.

By the way, I have a recovery tank not the expansion tank

I have found so many threads in LS1Tech regarding wiring cooling fans and AC with binary or trinary switches. Unfortunately, I could not find a clear schematic that shows wiring trinary switches with dual fans and compressor.

I am just sick of going through the cooling fans wiring, relays as I have to trace all the crapy wiring done by the stupid electrician. This may require dropping the vintage air evaporator just to trace one stupid wire.

Just do not feel like doing this as I have recently rearranged the big mess on the dash wiring, and I still cannot figure out why the stupid tach and speedometer on classic instruments do not work.

At least one fan should come on when you turn on the AC if you are using a binary switch. It has nothing to do with the engine temperature.

Don