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Fan switch sensor: replacement and selection

When and why a fan switch sensor needs replacement

The fan switch sensor has no specified lifetime limit. Most often replacement is performed after contacts oxidation.

Ingress of water in the engine compartment can be the cause of sensor defects. Influence of moisture affects contacts condition negatively.

Part defects can be indicated by unprompted activation of the fan when the ignition is turned on. Moreover, the fan stops switching on if the sensor is broken. Due to this temperature of the cooling liquid increases leading to engine overheating. Readings of a corresponding dashboard indicator show this.

It is recommended to visit a service station for part replacement. Cooling liquid should be drained before demounting of the radiator fan switch. In order to do this safely, you need a special coolant exchanger machine. Also, wires which supply electric current to the part need be to disconnected before servicing. A seal, which is often sold in a kit should be installed together with the sensor.

How to select a fan switch sensor

According to operation principle sensors are divided into three main types. A reservoir filled with wax is a basic element of the first type. It expands when heated and moves a pusher, which in turn activates the fan. The working element of devices of the second type is a bimetallic plate. It changes its shape when heated, which leads to closing a contact and, as a result, to activation of the fan. Electronic devices with a thermistor belong to the third type. Their operating principle is based on changes in thermistor electric resistance caused by changes in temperature. This is monitored by an electronic control module, which sends corresponding signals to the fan, turning it on or off.

Fan switch sensors for various car brands are produced by such manufacturers as Metzger, Vemo, Meyle, Facet. A required unit is selected in accordance with the car brand, model, production year as well as engine specifications and type of the fan installed. Pay attention that a certain temperature of sensor activation is specified for each car.

Size and pitch of the thread, quantity of connectors are important for proper installation of the part. Moreover, sensors can vary by mounting location. Often the part is mounted on the cylinder block, however, in some cars it is fastened in the lower part of a radiator.