Some of the factory GM wiring is the PCM can trigger the fans when it itself sees temp or need, but then there is a relay usually powered by a switch on the ac system exclusively for airflow through condensor when the defog system is on(Not a thing on square right?) and then also that is all with a PCM triggered compressor tho, usually. The 3800 had a run the fans at low speeds if temp A then run both at high at higher temp B
not your situation but figured to throw it out there
The 0411 ECU in the 01 firebird had a pressure sensor on the filter/drier that let the ECU read high side pressure. It would trigger the low speed fan output at a set high pressure and turn it off when it fell below a set pressure. You can program all of those pressures using a cheap tool and open source software. The Fan triggers can be programmed using engine coolant temp as well. They also have settings for on/off based on vehicle speed and other things.
In the square, until the EFI gets put in, I'm using the power feed to the AC clutch to activate the Fan 2 relay. The modern EFI will use ground triggers in the ECU to do essentially the same thing.
Airflow through the condenser is to allow the AC refrigerant to condense while the vehicle isn't moving and the AC system is on. Defrost usually runs the heater and AC together, since the AC evaporator is cold enough to condense the humidity in the air to dry it out, to provide warm dehumidified air to the windshield to keep it from getting condensation buildup. If the refrigerant doesn't condense before flowing to the evaporator, you don't get a state change in the evaporator and therefore your AC system doesn't work at all. This lets the high pressure side build more and more pressure and can cause your compressor to wear prematurely or even cause the pressure relief to blow.
