Electric Cooling Fan Control (3.0L)
Electric cooling fan circuits consist of one engine cooling fan, 2 auxiliary cooling fans, 2 temperature switches, A/C refrigerant pressure switch, Engine Control Module (ECM) cooling blower, timing control pump, auxiliary water pump, 5 fan control relays, one ECM relay, one auxiliary water pump relay and one engine cooling fan resistor. Relays are located at left front of engine compartment, in ECM housing. Auxiliary water pump is provided with battery voltage with ignition on, and when coolant temperature reaches 194°F (90°C).
At 212°F (100°C), primary temperature switch stage one contacts will close, enabling ECM relay (K48) and cooling fan control relay (K26) to energize. When ECM relay energizes, ignition voltage is applied to ECM cooling blower, allowing it to operate.
When cooling fan control relay (K26) energizes, battery voltage is applied to auxiliary cooling fan No. 1 and to auxiliary cooling fan No. 2 through the normally open contacts of fan control relay (K52). This allows auxiliary cooling fans to operate in series at half speed.
Fan control relay (K26) supplies battery voltage to engine cooling fan through the engine cooling fan resistor. The engine cooling fan resistor limits engine cooling fan operation to half speed. Fan control relay (K26) will also supply battery voltage to timing control pump through normally closed contacts of the auxiliary water pump relay (K22). This will allow timing control pump to operate.
Primary temperature switch stage one contacts will open when coolant temperature reaches 203°F (95°C). This will turn on all 3 fans, ECM cooling blower and turn the timing control pump off, unless A/C system is on.
If ignition switch is off and coolant temperature is greater than 212°F (100°C), both auxiliary cooling fans, engine cooling fan and timing control pump will remain on until coolant temperature drops to less than 203°F (95°C).
If temperature reaches 221°F (105°C), temperature switch contacts will close enabling fan control relays (K52 and K28) to energize. When fan control relay (K52) energizes, auxiliary cooling fan No. 1 runs at full speed as it is no longer in series with auxiliary cooling fan No. 2. When fan control relay (K28) energizes, battery voltage is applied to auxiliary cooling fan No. 2 which runs at full speed.
With primary temperature switch stage one contacts closed, ECM cooling blower, timing control pump and engine cooling fan (half speed) will continue to operate. Secondary temperature switch contacts will open when coolant temperature reaches 212°F (100°C) and cause operation of auxiliary cooling fans to operate differently as designated by primary temperature switch.
If coolant temperature reaches 230°F (110°C), secondary temperature switch stage 2 contacts will close, enabling fan control relay (K67) to energize. When fan control relay (K67) energizes, battery voltage is applied directly to engine cooling fan causing it to run at full speed. All other operations that were taking place before coolant temperature reached 230°F (110°C) remain in effect. Primary temperature switch stage 2 contacts open when coolant temperature reaches 221°F (105°C) and engine cooling fan will return to half speed.
At coolant temperatures greater than about 230°F (110°C), all 3 cooling fans run at full speed. ECM cooling blower, timing control pump and auxiliary water pump are also operating. Only 6 of the 7 relays operate at this time, unless A/C system is on. In this case, fan control relay (K87) and A/C compressor clutch relay (K60) will also operate.
To prevent excessively high refrigerant pressure, auxiliary cooling fans are switched from first speed to second speed at refrigerant pressures greater than about 276 psi (19.4 kg/cm2 ). When pressure drops to less than about 218 psi (15.3 kg/cm2 ), auxiliary cooling fans are switched back to first speed.