The engine cooling system consists of the following components:

Auxiliary Fans Low Speed, Electric Cooling Fan Low Speed, Water Auxiliary Pump

B+ is supplied to the heater water auxiliary pump whenever the ignition switch is in the ON position. When the engine temperature reaches 100°C (212°F), the primary cooling fan temperature switch stage 1 will close, enabling the fan control relay K26 to energize. When the fan control relay K26 energizes, B+ from fuse #52 is applied to the auxiliary coolant fan #1 (auxiliary engine coolant fan #1 is wired in series with auxiliary engine fan #2, through the normally closed contacts of the fan control relay K52). This will cause the auxiliary coolant fans #1 and #2 to operate at low speed. The fan control relay K26 will also supply B+ to the engine coolant fan resistor, voltage passes through the resistor to the electric coolant fan . The engine coolant fan resistor will cause the engine coolant fan to operate at low speed. The fan control relay K26 will also supply B+ to the water auxiliary pump through the auxiliary water pump relay K22, allowing the water auxiliary pump to operate. The primary cooling fan temperature switch stage 1 contacts will open when the coolant temperature reaches 95°C (203°F). This will turn all three fans and the auxiliary water pump OFF, unless the air conditioning system is ON.

If the ignition switch is in the OFF position and the engine coolant temperature is above 100°C (212°F), both of the auxiliary engine coolant fans #1 and #2, electric coolant fan, and the water auxiliary pump will remain ON until the coolant temperature drops below 95°C (203°F).

Auxiliary Fans High Speed

When the engine temperature reaches 105°C (221°F), the secondary cooling fan temperature switch contacts will close and energize the fan control relays K52 and K28. When the fan control relay K52 energizes, it will ground terminal B of auxiliary engine coolant fan #1. Terminal A of the auxiliary engine fan #1 still receives B+ from fan control relay K26. The auxiliary coolant fan #1 is no longer in series with the auxiliary engine coolant fan #2 and will now operate at full speed. When the fan control relay K28 is energized, B+ from fuse #40 will be applied to terminal A of the auxiliary engine coolant fan #2. The auxiliary coolant fan #2 is no longer in series with the auxiliary engine coolant fan #1 and operates at full speed. Terminal B of the auxiliary coolant fan #2 is permanently grounded to G103. With the stage 1 contacts of the primary cooling fan temperature switch closed, the water auxiliary pump, and the electric cooling fan will continue to operate. The secondary cooling fan temperature switch contacts will open when the coolant temperature reaches 100°C (212°F). This will cause the auxiliary engine coolant fans #1 and #2 to operate at low speed.

Electric Coolant Fan High Speed

When the engine coolant temperature reaches 110° (230°F), the primary cooling fan temperature switch stage 2 will close energizing the fan control relay K67. When the fan control relay K67 energizes, B+ from fuse #42 will be applied directly to terminal A of the engine coolant fan ( bypassing the engine coolant fan resistor ) and the engine coolant fan will operate at full speed. All the other operations that were taking place before the coolant temperature reached 110°C (230°F) will remain in effect. The primary cooling fan temperature switch stage 2 contacts will open when the coolant temperature reaches 105°C (221°F) and the primary engine coolant fan will return to half speed.

At coolant temperatures above approximately 110°C (230°F), all three coolant fans are operating at full speed. The water auxiliary pump and the heater water auxiliary pump are also operating. Only five of the six relays operate at this time, unless the air conditioning system is turned ON. In this case, the fan control relay K87 and the A/C compressor relay K60 will also operate.

Engine Cooling Fans (A/C Operation)

When the A/C compressor is turned on, fan control relay K87 is energized and the auxiliary engine coolant fans # 1 and #2 will operate in low speed. In order to prevent inadmissible high refrigerant pressure in the refrigerant circuit, the auxiliary engine coolant fans #1 and #2 are switched from the low speed to the high speed at refrigerant pressures above approximately 1,900 kPa (275 PSI). When the pressure drops below approximately 1,500 kPa (217 PSI), the auxiliary engine coolant fans #1 and #2 are switched back to the low speed.