PTC Heater (Where Fitted) (Heating and ventilation)

PTC Heater (Where Fitted)

The PTC heater operates while the engine is running and, for a limited period, if the ignition is switched on without starting the engine.

When the ignition switch is turned to position II, the ECM energises the fuel pump relay, which, in addition to connecting power supplies to the fuel pumps, connects a power supply to the coil of the power relay in the PTC heater system. The ECM keeps the fuel pump relay energised while the engine is running. If the engine is not started within approximately 60 seconds of turning on the ignition, the ECM de-energises the fuel pump relay.

The earth side of the power relay coil is connected to earth via the contacts of the control relay. The coil of the control relay is connected in series to the heater switch, blower switch and ignition switch. While the ignition switch is in position II, if the blower is selected on and the temperature control is turned clockwise to a position past 1 o’clock, a power supply is connected to the coil of the control relay. The control relay energises and connects the coil of the power relay to earth, which then energises and connects power to the PTC heater.

On manual gearbox models, when the control relay is energised a power feed is connected to the ECM. When the ECM senses the power feed, if the engine coolant temperature is below 85 °C (185 °F) it increases engine idle speed by 50 rev/min, to improve idle speed refinement while the additional load is imposed on the alternator by the PTC heater.