A/C request

Fusible link 4 (C0570) and fusible link 5 (C0573) of the under bonnet fuse box provide the ignition switch (C0028) with permanent feeds on NP and NW wires respectively. When the ignition switch is in position II, feeds are connected from the ignition switch to:

Fuse 15 (C0099) of the passenger compartment fuse box on a Y wire. From fuse 15 (C0585), the feed is connected to the A/C relay pack (C0173), A/C switch pack (C0275), fresh/ recirculated air switch (C0750) and fresh/ recirculated air mode motor (C0413) on LGS wires. Fuse 24 (C0595) of the satellite fuse box on a WLG wire. From fuse 24 (C0595), the feed is connected to the blower motor (C0056) on a LGP wire and from the blower motor (C0056) to the blower motor switch (C0058) by a SB wire. When the blower is selected to positions 1 to 4, the feed is supplied from the blower switch (C0058) to the A/C switch pack (C0275) on a SW wire.

A/C request

When the A/C switch is pressed, while one of the four blower speeds is selected, SK wires connect the power feed from the A/C switch pack (C0275) to the A/C thermostat (C0422) and from the A/C thermostat (C0423) to the trinary switch (C0279). Provided the high and low temperature switches are closed, the trinary switch (C0279) then supplies the power feed to the ECM (C0159) on a UR wire. With A/C selected on, the tell tale illumination LED in the A/C switch pack (C0275) is earthed on the B wire, connected to an earth header (C0017), and illuminates.

When the ECM receives an A/C request, it energises the appropriate relays in the A/C relay pack to operate the compressor, cooling fan and condenser fan.

The high and low switches in the trinary switch guard against extremes of pressure in the refrigerant system. If refrigerant system pressure reaches either of the limits, the related switch opens and disconnects the A/C request to the ECM. The air temperature sensor detects evaporator matrix temperature and, if the temperature is less than 2 °C (36 °F), opens and disconnects the A/C request to the ECM.

Compressor

To operate the compressor, the ECM earths the UB wire between the ECM (C0159) and the coil of the compressor clutch relay in the A/C relay pack (C0173). The energised compressor clutch relay connects the power feed from fuse 5 in the under bonnet fuse box to the R wire between the A/C relay pack (C0172) and the A/C compressor clutch (C0127). The A/C compressor clutch is earthed through the compressor fixings and energises to transmit drive to the compressor.