Radiator Cooling Fan Motor: Description and Operation

The Powertrain Control Module (PCM) controls both Cooling Fans by controlling three relays through two outputs. There are two modes of cooling fan operation: low speed and high speed. In the low speed mode, the cooling fans are powered in series. Cooling Fan 1 Relay is energized by the PCM and both cooling fans run at low speed. In the high speed mode the cooling fans are powered in parallel which allows the fans to run at high speed. Cooling fans operate only when the ignition is in RUN.

Low Speed Conditions
The PCM turns on the cooling fans at low speed when the engine coolant temperature exceeds 106°C. The cooling fans turn off when the engine coolant temperature falls below 98°C. The PCM monitors engine coolant temperature using the engine coolant temperature sensor input on CKT 410.

The Heater and A/C Programmer requests the PCM to turn on the cooling fans at low speed through the UART data line when the A/C high side refrigerant temperature exceeds 50°C.The Programmer requests that the cooling fans turn off once the A/C high side refrigerant temperature falls below 47°C.

The Heater and A/C Programmer also requests low cooling fan speed operation when all of the following conditions are met:
1. Vehicle speed is below 20 mph.
2. A/C Compressor Clutch engagement is possible.
3. Outside air temperature is greater than 7°C.

Low Speed Operation
Low speed cooling fan operation occurs when the PCM grounds the Cooling Fan 1 Relay coil on CKT 335. With only Cooling Fan 1 Relay energized, voltage is applied to both the Pusher and Puller Cooling Fan Motors. The voltage path to the motors is through the Cooling Fan 1 Relay contacts, CKTs 532, 504 and 409, and the Cooling

Fan 2 Relay contacts. The two motors are connected to each other through a series circuit. This causes the voltage applied by Maxi(R) Fuse 3 to be divided between the two motors. The division of the voltage causes the motors to operate at a lower speed. In the series mode, the fans are grounded through CKT 250 and ground G104.

High Speed Conditions
The PCM turns on the cooling fans at high speed when the engine coolant temperature exceeds 108°C or the Engine Coolant Temperature Sensor circuit has failed. The PCM switches the cooling fans to low speed operation once the engine coolant temperature falls below 106°C.

The Heater and A/C Programmer requests the PCM to turn on the cooling fans at high speed through the UART data line if the A/C high side refrigerant temperature exceeds 57°C or an A/C High Side Temperature Sensor circuit failure occurs. The Heater and A/C Programmer requests that the cooling fans be switched to low speed operation when the A/C high side refrigerant temperature falls below 51°C.

High Speed Operation
The cooling fans run at high speed when the PCM energizes Cooling Fan 1, 2 and 3 Relays on circuits 473 and 335 by grounding the relay coils. With Cooling Fan 1 Relay energized, battery voltage is applied to the Pusher Cooling Fan Motor through the relay contacts. The Pusher Cooling Fan Motor runs at high speed because the fan motor is grounded directly through the contacts of the Cooling Fan 2 Relay, CKT 250 and ground G104.

Since Cooling Fan 3 Relay is also energized during high speed operation, battery voltage is applied directly to the Puller Cooling Fan Motor through the closed contacts of the relay. The Puller Cooling Fan Motor runs at high speed since it is no longer in series with the Pusher Cooling Fan Motor.