Preliminary Information

Principle Wiring Diagram





Checking Heating and Evaporator Temperature Regulation.





The inside temperature of the car can be adjusted with the heating regulation control knob (1).

A so-called "control range" is between both end positions of the heating regulator (control unit). A temperature (nominal value) set in this range will be regulated by the control unit. The temperature inside of the car and the heater blowing out temperature are measured with one each temperature sensor and compared with the given nominal value in the control unit. A valve in the feed of the hot water circuit will be opened more or less long depending on the amount of deviation from the nominal value and the temperature inside of the car it regulated in this manner. The water valve is operated electromagnetically. The electric control of the water valve is designed that the water valve will be opened and therefore maximum heating will be provided, if the electrical system would fail (e.g. faulty control unit). In case of malfunctioning and/or failure of the heating regulation system, defects must be found in the system with the following test plan.

The heating and evaporator temperature regulation corresponds with the previously described heating regulation when the air conditioner is switched off. Heating regulation and the heater blower do not work when the air conditioner is switched on.

The A/C compressor clutch is activated by the evaporator temperature regulator, which works in accordance with the evaporator temperature sensor and heating regulator (control unit).