Opel Corsa B 1993–2000 Service and Repair Manual: Cooling system electrical switches - testing, removal and refitting

Electric cooling fan thermostatic switch

Testing

1. Testing of the switch as part of the fan test procedure.

Removal

2. The switch is located in the side of the radiator (see illustration). The coolant should be cold before removing the switch.

Cooling fan thermostatic switch screwed into side of radiator

3. Disconnect the battery negative lead. If necessary, firmly apply the handbrake then jack up the front of the vehicle and support it on axle stands. Access to the switch can then be gained from underneath the vehicle.

4. Either drain the cooling system to below the level of the switch, 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.

6. Carefully unscrew the switch from the radiator and recover the sealing ring/washer.

Refitting

7. Refitting is a reversal of removal using a new sealing ring/washer. Securely tighten the switch and top-up/refill the cooling system.

8. On completion, 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 sender

Testing

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

10. The sender is located in the cylinder head, behind the water pump on 1.2 litre engines, in the inlet manifold on 1.3 and 1.4 litre engines, and in the thermostat housing on 1.6, 1.8 and 2.0 litre engines (see illustration). The sender 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 sender resistance is high, current flow through the gauge is reduced, and the gauge needle points towards the `cold' end of the scale. If the sender is faulty, it must be renewed.

Disconnecting the temperature gauge sender wire (1.8 litre model shown)

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 voltage stabiliser, which will necessitate renewal of the stabiliser. 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 sender wire, and earth it to the cylinder head. If the needle then deflects when the ignition is switched on, the sender unit is proved faulty, and should be renewed. If the needle still does not move, remove the instrument panel and check the continuity of the wiring between the sender 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 the gauge unit should be renewed.

13. If the gauge needle remains at the `hot' end of the scale, disconnect the sender wire.

If the needle then returns to the `cold' end of the scale when the ignition is switched on, the sender 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 sender, or have ready a suitable plug which can be used to plug the sender aperture whilst it is removed. If a plug is used, take great care not to damage the sender unit threads, and do not use anything which will allow foreign matter to enter the cooling system.

15. Disconnect the battery negative lead.

16. Disconnect the wiring from the sender, then unscrew the unit from its location.

Refitting

17. Ensure that the sender threads are clean and apply a smear of suitable sealant to them.

18. Refit the sender, tightening it securely, and reconnect the wiring.

19. Top-up the cooling system as described in "Weekly checks" 20 On completion, start the engine and check the operation of the temperature gauge. Also check for coolant leaks.