Radiator Cooling Fan Temperature Sensor / Switch: Description and Operation

DESCRIPTION

These models use two cooling fans, two thermo sensors and four relays to control the cooling fan operation.
With A/C off and engine coolant temperature below 194°F, the cooling fans will not operate. When coolant temperature exceeds 194°F, thermo sensor No. 1 closes and No. 1 cooling fan operates at low speed (1400 RPM). When coolant temperature reaches 212°F, thermo sensor No. 2 closes and cooling fan No. 1 operates at high speed (2000 RPM) while cooling fan No. 2 operates at its one speed (1700 RPM).
With A/C control on, compressor off, thermo sensor No. 1 open or closed and coolant temperature below 212°F, No. 1 cooling fan will operate at low speed. When coolant temperature reaches 212°F, thermo sensor No. 2 closes and cooling fan No. 1 will operate at high speed while cooling fan No. 2 operates at its one speed.
With A/C control on, compressor on and engine coolant below 212°F, cooling fans No. 1 and 2 will operate. If blower motor voltage is below 9 volts, fan No. 1 will operate at low speed. If blower motor voltage increases to 9 volts or more, No. 1 cooling fan will operate at high speed.
With A/C control on, compressor on and engine coolant above 212°F, both fans operate at maximum speed.

THERMO SENSOR

Replace

Fig. 7 Electric engine cooling fan assembly. 1985-88 Maxima:

Thermo sensor No. 1 is located in the radiator lower tank. Thermo sensor No. 2 is located in the radiator upper tank, Fig. 7.



1. Disconnect battery ground cable.
2. Drain cooling system into suitable container.
3. Disconnect thermo switch wiring, then remove switch.
4. Reverse procedure to install.

Fig. 1 Testing thermo switch (typical):

Testing

1. Remove thermo switch as outlined above.
2. Connect suitable ohmmeter across switch terminals, then immerse lower part of switch in water, Fig. 1. Ohmmeter should indicate an open circuit.
3. Place thermometer in water and heat. When water temperature reaches approximately 194°F for thermo sensor No. 1 or 212°F for thermo sensor No. 2, switch contacts should close and the ohmmeter should indicate continuity.
4. If switch does not operate properly, replace it.