Electric Cooling Fans
Electric cooling fan circuits consist of one engine cooling fan, 2 auxiliary cooling fans, 2 temperature switches, A/C compressor refrigerant pressure switch, Engine Control Module (ECM) cooling blower, timing control pump, auxiliary water pump, 7 fan control relays, 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 at all times, enabling it to operate any time ignition switch is on.
At 212°F (100°C), temperature switch No. 1 stage one contacts will close, enabling ECM relay (K48) and cooling fan control relay (K26) to energize. When ECM relay energizes, ignition voltage will be 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 will cause auxiliary cooling fans to operate in series at half speed.
Fan control relay (K26) will also supply battery voltage to engine cooling fan after it goes through the engine cooling fan resistor. The engine cooling fan resistor will cause engine cooling fan to operate at 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.
Temperature switch No. 1 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 the A/C system is on.
If ignition switch is off and coolant temperature is above 212°F (100°C), both auxiliary cooling fans, engine cooling fans and timing control pump will remain on until coolant temperature drops below 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 will go to 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 operates at full speed.
With temperature switch No. 1 stage one contacts closed, ECM cooling blower, timing control pump and engine cooling fan (half speed) will continue to operate. Temperature switch No. 2 contacts will open when coolant temperature reaches 212°F (100°C) and cause operation of auxiliary cooling fans to operate differently as designated by temperature switch No. 1.
If coolant temperature reaches 230°F (110°C), temperature switch No. 2 stage two contacts will close, enabling fan control relay (K67) to energize. When fan control relay (K67) energizes, battery voltage will be applied directly to engine cooling fan causing it to operate at full speed. All other operations that were taking place before coolant temperature reached 230°F (110°C) will remain in effect. Temperature switch No. 1 stage two contacts will open when coolant temperature reaches 221°F (105°C) and engine cooling fan will return to half speed.
At coolant temperatures above about 230°F (110°C), all 3 cooling fans operate 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 turned on. In this case, fan control relay (K87) and A/C compressor 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 above about 276 psi (19.4 kg/cm2 ). When pressure drops below about 218 psi (15.3 kg/cm2 ), auxiliary cooling fans are switched back to first speed.