Component Operation

1. Heater/ A/C unit
The heater/ A/C unit includes the fresh-air, by-pass air, defroster and footwell flaps, the two blowers and particle filters and the evaporator (on vehicles fitted with A/C system). In the heater/ A/C unit, the heating/air conditioning regulator mixes and distributes fresh air, cold air (on vehicles with A/C system) and hot air according to the preset values.

1.1 Final stage
The final stage connects the heater units to ground. Ground signals are clocked with a frequency of 30 Hz. The speed of the heater blowers is determined by the pulse-to-pause ratio.

2. Heater/ A/C regulator
The heater/ A/C regulator includes the closed-loop and open-loop control electronics, the interior sensor complete with blower as well as a number of potentiometers and switches that are used to actuate the flaps. The heater/ A/C regulator controls the setting of the individual flaps in accordance with the temperature preset at the potentiometer, interior temperature, vehicle speed and hot air temperature.

3. Temperature mixing flaps
The temperature mixing flaps are used to control the supply (quantity) of hot air.

4. Auxiliary blower
At low engine speeds, the auxiliary blower ensures supply of sufficient air and provides a resistance at higher engine speeds. This produces an air mass map that facilitates temperature control.

4.1 Temperature sensor for auxiliary blower
A variable resistor (NTC) used to detect the engine cooling air temperature. It is used to control the auxiliary blower.

4.2 Series resistor for auxiliary blower
Reduces the blower speed of the first stage. A built-in bimetal fuse protects the series resistor against overloads. If the bimetal fuse is triggered, a restart interlock prevents overloading the resistor after it has cooled off. This allows the cause for any overload, e.g. a binding blower, to be detected.

5. Heater flap box
Excess hot air that is not required is evacuated to the outside across the heater flap boxes.

To keep exhaust fumes from entering the system, the outlet openings are fitted with rubber flaps that close automatically.
6. Condenser
Transforms the gaseous refrigerant into a fluid state.

6.1 Condenser blower
This blower is used to cool down the refrigerant.

6. 2. Series resistor for condenser blower
Reduces the blower speed of the first stage.