Cooling systen electical switches - testing, removal and refitting

Cooling, heating and ventilation systems / Cooling systen electical switches - testing, removal and refitting

Electric cooling fan thermostatic Testing
1 Testing the switch is described in Section 5, as part of the cooling fan test procedure.

Removal
2 The switch is located in the left-hand side of the radiator. The engine and radiator should be cold before removing the switch.

3 Disconnect the battery negative lead. Note: Make sure you know the anti-theft code for the radio so that it can be reactivated later.

4 Either drain the cooling system to below the level of the switch (as described in Chapter 1), or have ready a suitable plug which can be used to plug the switch aperture in the radiator whilst the switch is removed. If a plug is used, take great care not to damage the radiator, and do not use anything which will allow foreign matter to enter the radiator.

5 Disconnect the wiring plug from the switch (see illustration).

6.5 Cooling fan motor thermoswitch

6 Carefully unscrew the switch from the radiator. Recover the washer.

Refitting
7 Refitting is a reversal of removal, but fit a new washer and tighten the switch to the specified torque setting. On completion, refill the cooling system as described in Chapter 1 or top-up as described in “Weekly checks”.

8 Start the engine and run it until it reaches normal operating temperature, then continue to run the engine and check that the cooling fan cuts in and functions correctly.

Coolant temperature gauge sensor
Testing
9 The coolant temperature gauge, mounted in the instrument panel, is fed with a stabilised voltage supply from the instrument panel feed (through the ignition switch and a fuse), and its earth is controlled by the sensor.

10 The sensor unit is clipped into the coolant outlet housing on the left-hand end of the cylinder head (see illustration). The sensor contains a thermistor, which consists of an electronic component whose electrical resistance decreases at a predetermined rate as its temperature rises. When the coolant is cold, the sensor resistance is high, therefore current flow through the gauge is reduced, and the gauge needle points towards the “cold” end of the scale. If the sensor is faulty, it must be renewed.

6.10 Coolant temperature gauge sensor clipped into the coolant outlet housing on the left-hand end of the cylinder head

11 If the gauge develops a fault, first check the other instruments; if they do not work at all, check the instrument panel electrical feed.

If the readings are erratic, there may be a fault in the instrument panel assembly. If the fault lies in the temperature gauge alone, check it as follows.

12 If the gauge needle remains at the “cold” end of the scale, disconnect the wiring connector from the sensor unit, and earth the temperature gauge wire (see “Wiring diagrams” for details) to the cylinder head. If the needle then deflects when the ignition is switched on, the sensor unit is proved faulty, and should be renewed. If the needle still does not move, remove the instrument panel (Chapter 12) and check the continuity of the wiring between the sensor unit and the gauge, and the feed to the gauge unit. If continuity is shown, and the fault still exists, then the gauge is faulty and should be renewed.

13 If the gauge needle remains at the “hot” end of the scale, disconnect the sensor wire.

If the needle then returns to the “cold” end of the scale when the ignition is switched on, the sensor unit is proved faulty and should be renewed. If the needle still does not move, check the remainder of the circuit as described previously.

Removal
14 Either partially drain the cooling system to just below the level of the sensor (as described in Chapter 1), or have ready a suitable plug which can be used to plug the sensor aperture whilst it is removed. If a plug is used, take great care not to damage the sensor unit aperture, and do not use anything which will allow foreign matter to enter the cooling system.

15 Disconnect the wiring from the sensor.

16 Depress the sensor unit and slide out its retaining clip. Withdraw the sensor from the coolant elbow and recover its sealing ring.

Refitting
17 Fit a new sealing ring to the sensor unit.

Push the sensor fully into the coolant elbow and secure it in position with the retaining clip.

18 Reconnect the wiring connector then refill the cooling system as described in Chapter 1 or top-up as described in “Weekly checks”.