Thermo switch

Thermo switch

The thermo switch will switch the compressor on and off dependent on the temperature of the air passing through the evaporator. The thermo switch will allow the compressor to operate when it detects that the evaporator temperature is 5C or above and will switch the compressor off when the evaporator temperature drops to 2C by breaking the earth path to the aircon sense. When the evaporator temperature is above 5C the closed thermo switch completes the earth path to the aircon sense.

NOTE: When the air conditioning is switched on the MEMS ECU will delay the switching of the compressor clutch until the stepper motor has indexed a predetermined amount of additional steps preventing a sudden drop in engine speed when the clutch is operated.

If the coolant temperature or the air-conditioning system pressure continues with the fans on slow speed, either the medium pressure switch or the high engine temperature switch will operate.

Bosch ECM

This will provide a direct path to earth via the U/Y wire to the cooling fan relay and the condenser fan relay 1 to achieve operation at high speed (fans connected in parallel).

Non-Bosch ECM

This will provide an earth to the ECM on the Y/B wire. As a result the ECM provides an earth via the U/Y wire to the cooling fan relay and the condenser fan relay 1 to achieve operation at high speed (fans connected in parallel).

NOTE: The compressor clutch relay is connected internally to the cooling fan relay causing slow speed cooling when the clutch is engaged.

Low temperature switch (Bosch ECM only)

The low temperature switch provides an earth to the cooling fan relay when the engine temperature reaches 105C. With the relay energised a feed can pass from fuse 4 in the engine compartment fuse box to the closed contacts of the condenser fan relay 2 (within the relay module) to provide feed to the condenser fan motor on a P/S wire.