Cooling Fan Thermal Switch — Checking, Removing and Installing (Audi 100 C3)

1. If the thermal switch at the base of the radiator is damaged, the most likely cause is a circuit failure. The fan motor does not turn on even if the coolant reaches operating temperature.

2. To check the thermal switch, disconnect the wiring and connect the connector clamps. The fan should work (even without the ignition on), in this case, the thermal switch is faulty and must be replaced.

3. Before removing the thermal switch, first drain the cooling system as described in Chapter 3.

4. Disconnect the negative battery terminal.

5. Disconnect the electrical wiring, unscrew the thermal switch from the radiator, remove the sealing washer.

6. To check the operating temperature of the thermal switch, immerse it in a pan of water so that only the screw end of the switch is immersed, the electrical contacts should not be in the water. Connect an ohmmeter between the terminals of the switch, or a battery and an incandescent lamp in series with the switch. Place a thermometer in the pan, heat the water, and record the temperature at which the switch closes. Allow the water to cool and note the temperature at which the switch contacts open. If the operating temperatures are not within the range specified in the Specifications, replace the switch.

7. Installation is carried out in reverse order, always use a new sealing washer. Fill the cooling system as described in Chapter 5.