[BNaylor]

The PCM module uses the A/C hi/lo pressure switch to turn on the cooling fans in conjunction with monitoring engine temperature through the engine coolant temperature sensor (ECT). So if the A/C system is not charged the cooling fans may not turn on when the A/C is on. The fans should turn on in low speed at around 225 degrees and hi-speed at 230 degrees. The same ECT sensor is also used to display engine temperature on the IP gauge.

If you are in the red zone then find the cause for the overheating. Could be a bad thermostat, LIM gaskets, or the cooling system needs a flush and new coolant.

A simple test is to disconnect the ECT sensor and see if the fans turn on. With engine off remove the electrical connector to the ECT located by the thermostat on left side of engine. Then start engine. Fans should turn on in about 5 seconds. That way you can see if the ECT is the cause, wiring, PCM module or cooling fan control relays, etc.