Heated Front Screen (HFS)

HEATED FRONT SCREEN (HFS)

DESCRIPTION

General
Operation of the Heated Front Screen (HFS) is controlled by the Automatic Temperature Control (ATC) ECU via the non latching HFS switch.

When the engine is running and the HFS is selected, the ATC ECU illuminates the LED above the switch and energises the HFS relay attached to the passenger end of the fascia cross tube. If not already active, the ATC ECU also activates the N C compressor and the blower, and sets air distribution to windscreen. After 10 minutes (when ambient temperature is -15 °C (50 °F ) or above) or 17 minutes (when ambient temperature is less than -15 °C (5 °F)), the ATC ECU extinguishes the LED and de-energises the heated front screen relay. After the heater times out or is switched off, the timer in the ATC ECU is reset to zero.

OPERATION

Power Distribution
Feed from the positive battery terminal (C0192) is supplied to fusible link 1 and fuse 53 of the passenger compartment fuse box (C0632) on an R wire. Fusible link 1 (C0592) provides a constant battery feed to the HFS relay (C0994) on an R wire.

Fuse 53 (C0583) provides a constant battery feed to the ignition switch (C0028 on V8 vehicles) on an R wire. When the ignition switch is turned to the 'ignition' position, current flows across the switch (C0028 on V8 vehicles) to fuse 34 of the passenger compartment fuse box (C0585) on a G wire. Fuse 34 (C0587) provides an ignition feed to the HFS relay coil (C0994) on a GY wire. The earth path for the relay coil (C0994) is controlled by the ATC ECU (C1629) on a UN wire.

HFS
When the HFS switch is pressed, a momentary earth path (C1630) is created on an N wire. If all operational conditions are met (see 'Description' above), the ATC ECU energises the HFS relay. The energised HFS relay (C0994) provides a feed to the LH (C0247) and RH (C0246) heater elements on a pair of B wires. Both elements are earthed on N wires.