Voltage Signal: Description and Operation

OPERATION
The electric cooling fans are used to cool engine coolant flowing through the radiator. They are also used to cool the refrigerant (R134a) flowing through the AIC condenser.

DESCRIPTION
Power for the cooling fan motors is supplied by the Cooling Fans Maxi-Fuse. The relays are energized when the PCM grounds the fan control driver circuits. The PCM Output Driver Module (0DM) B output 1 (low speed fan control circuit) is grounded for Low Speed fan operation. PCM 0DM B outputs 1 (low speed fan control circuit) and 2 (high speed fan control circuit) are grounded for High Speed operation.

The cooling fan system on this vehicle consists of a single speed right side cooling fan and a dual speed left side cooling fan. While in low speed operation, CKT 409 supplies battery feed directly to the right side cooling fan motor. The left side cooling fan motor is supplied a feed through a resistor, causing it to run at low speed. When high speed operation is commanded, the right side fan continues to run at low speed; but CKT 532 supplies a feed directly to the left side cooling fan motor, causing it to run at high speed.

The PCM commands low speed fans operation when the following conditions are present:
- Vehicle speed is less than 58 mph.
- Engine coolant temperature is above 1OO°C (212°F).

OR

- Vehicle speed is less than 40 mph.
- Intake air temperature is above 9°C (48°F).
- AC refrigerant pressure is greater than 190 psi (1300 kPa).

High speed fan operation is commanded when the following conditions are present:
- Vehicle speed is less than 65 mph.
- Engine coolant temperature is above i08°C (226°F).