Radiator Fan Control Module

Fig 41 Fan Control Module:

The radiator fan runs at a variable speed depending on coolant temperature and A/C system pressure. The radiator fan circuit contains a Pulse Width Module (PCM).

A 5 volt signal is supplied to the PCM. The PCM provides a pulsed ground for the PCM. Depending upon the amount of pulse on time, the PCM puts out a proportional voltage to the fan motor at the lower speed. For instance, if the on time is 30 percent, then the voltage to the fan motor will be 3.6 volts.

When engine coolant reaches approximately 102°C (215°F) the PCM grounds the PCM relay.
- If engine coolant reaches 207°C (225°F) the PCM grounds the high speed ground relay and high speed fan relay.
- If the fan operates at high speed, the PCM de-energizes the high speed relay and high speed ground relay when coolant temperature drops to approximately 101°C (214°F).
- When coolant temperature drops to 101°C (214°F) the fan operates at low speed.
- The PCM de-energizes the low speed relay when coolant temperature drops to approximately 93°C (199°F).

Also, when the air conditioning pressure switch closes, the fan operates at high speed. The air conditioning switch closes at between 275 and 295 psi.
- When air conditioning pressure drops approximately 40 psi, the pressure switch opens and the fan operates at low speed.

The PCM relay is located on the left front inner frame just behind the radiator (Fig. 41).