Chart C-12 Coolant Fan Control Circuit (With A/C)
Chart C-12 - Coolant Fan Control Circuit With A/C (Part 1 of 2):
Wiring Diagram for Chart C-12 - Coolant Fan Control Circuit With A/C:
CHART C-12 - COOLANT FAN CONTROL CIRCUIT WITH A/C (PART 1 OF 2)
Circuit Description:
Battery voltage, CKT 2, is supplied to the fan control relay terminal "E" and to the timer relay terminal "7". Ignition voltage, CKT 250, is supplied to the fan control relay terminal "C" and to the timer relay terminal "5".
The ECM controlled A/C fan relay, when energized, grounds CKT 335 and fan control relay terminal "B". This energizes the fan control relay, closing its contacts and supplying battery voltage to the fan motor.
If the ignition switch is turned "OFF" and the fan temperature switch is closed, the fan timer relay will continue to supply battery voltage to the cooling fan CKT 903 and the low speed resistor. The fan will run on low speed for about 5 minutes if the temperature switch remains closed and the ignition "OFF."
^ ECM control
^ A/C "ON".
^ Vehicle speed less than 35 mph.
^ CKT 409 to A/C fan relay terminal "C" grounded by ECM at terminal "C1".
^ Coolant temperature less than 110~C.
^ After-run timer relay control
^ Ignition "OFF."
^ Coolant temperature above 105~C.
^ Fan temperature switch closed grounding CKT 904.
^ Timer relay closed supplying battery voltage to CKT 903.
^ Coolant temperature control
^ Coolant above 110~C.
^ Temperature switch closed grounding CKT 904 and timer relay terminal "3".
^ Ignition "ON."
^ Timer relay module terminal "6" grounding CKT 335 to fan control relay terminal "B".
Test Description: Numbers below refer to circled numbers on the diagnostic chart.
1. Checks for the fan timer relay sticking "ON" causing a low battery condition.
2. Checks fan motor, timer relay, CKTs 335, 250, and 904.
3. The delay relay supplies a current limited 12 volts to terminal "1". The ignition switch will ground terminal "1" in crank position. Making the test with auto transmission in "drive" or manual with clutch released will prevent starter engagement during the test. If the ignition switch is "OFF," the relay should allow the fan to run low speed for about 5 minutes. This would be the time to check the timer feature, if it is considered part of the problem.
Chart C-12 - Coolant Fan Control Circuit With A/C (Part 2 of 2):
CHART C-12 - COOLANT FAN CONTROL CIRCUIT (WITH A/C) (PART 2 OF 2)
Circuit Description:
Solenoids and relays are turned "ON" or "OFF" by the ECM, using internal electronic switches called "drivers." Each driver is part of a group of four called "quad-drivers." Failure of one can damage any other driver within the set.
Solenoid or relay coil resistance must measure more than 20 ohms. Less resistance will cause early failure of the ECM driver.
Before replacing the ECM, be sure to check the coil resistance of all solenoids and relays controlled by the ECM. See ECM wiring diagram for the solenoids and relays and the coil terminal identification.
When checking TCC solenoid, be sure to raise drive wheels and run above 30 mph to close third gear apply switch, if used.