Chart C-12C Coolant Fan Functional Check (No High Speed)

Chart C-12C - Coolant Fan Functional Check (No High Speed):

Wiring Diagram for Chart C-12C - Coolant Fan Functional Check (No High Speed):

CHART C-12C - COOLANT FAN FUNCTIONAL CHECK (NO HIGH SPEED)

Circuit Description:

On V08 (Heavy Duty Cooling) systems, the two coolant fans are energized through one low speed and two high speed relays. On standard cooling applications, one fan, one low speed relay and one high speed relay are used.

Power for the fan(s) comes through the fusible link to terminal "1" on all relays. The relays are energized when current flows to ground through the activation of the A/C pressure and coolant temperature switches, and/or the ECM.

Low Speed Relay - The Low Speed Relay is energized by the ECM or the A/C pressure switch. The ECM energizes the relay through terminal "D2" when the coolant temperature reaches 98°C (208°F) and vehicle speed is below 45 mph. The Low Speed Relay is also energized through the A/C pressure switch through terminal "B" when refrigerant pressure reaches 1034 kPa (150 psi).

High Speed Relay - The High Speed Relay is energized by the A/C high pressure and coolant switches. If the A/C refrigerant pressure reaches 1896 kPa (275 psi) or the coolant temperature reaches 108°C (226°F) the High Speed Fan Relay is energized. The ECM has no control of the High Speed Fan Relay.

The Pusher Fan Relay - The Pusher Fan is installed as part of the heavy duty cooling package (VO8) and is turned "ON" anytime the high speed fan is running. When the A/C pressure reaches 1896 kPa (275 psi) or the coolant temperature reaches 108°C (226°F) both fans are energized. The ECM has no control of the Pusher Fan Relay.




Test Description: The following numbered steps correspond with the step numbers on the diagnostic chart.

1. Jumping harness terminal "1" to "4" bypasses the relay and fan should run.

2. Grounding the coolant temperature switch circuit allows current to flow to ground and light the test light.