Heating push-button control unit, task - GF83.20-P-2120-02PP

Fig 1: Identifying Heating Push-Button Control Unit

The following settings can be performed on the HEAT [HAU] control and operating unit (N18):

Interior temperature using the left temperature selector wheel (2) or right temperature selector wheel (3)
Air volume using the blower switch (1)
Air distribution using the air distribution switch (4)
Air recirculation mode by pressing the air recirculation switch (N18s2)
Defrost function by pressing the defroster button (5)
Control of the heated rear window by pressing the heated rear window switch (N18s1)

The HEAT control and operating unit (N18) has diagnostic capability. As a result, any faults which occur are stored in a fault memory which can be read out using STAR DIAGNOSIS.

The HEAT [HAU] control and operating unit (N18) controls all actuators of the automatic heater (HEAT [HAU]).

The HEAT control and operating unit (N18) reads in the following signals via the Controller Area Network bus class B (interior) (CAN-B):

ambient air temperature sensor
in-car temperature sensor (up to 31.5.02) via the overhead control panel control unit
battery voltage, coolant temperature sensor and engine speed via the EIS [EZS] control unit
ground speed via the instrument cluster

The interior temperature of vehicles as of 1.6.02 is measured exclusively by the in-car temperature sensor integrated in the HEAT [HAU] control and operating unit (N18).

Blower switch (1)

The blower switch (1) controls the output of the blower motor. The blower switch (1) switches the control voltage for the blower regulator in 6 stages and 4 intermediate positions via the HEAT [HAU] control and operating unit (N18). As a result, a blower speed of 0 - 100 % is achieved.

Left temperature selector wheel (2) and right temperature selector wheel (3)

The left temperature selector wheel (2) and the right temperature selector wheel (3) serve to preselect the desired interior temperature. By turning it, the desired interior temperature is set separately for the left and right sides. The HEAT [HAU] control and operating unit (N18) compares the desired temperature with the current interior temperature which is measured by the in-car temperature sensor (up to 31.5.01) in the overhead control panel control unit.

Based on the comparison between specified and actual values, the HEAT [HAU] control and operating unit (N18) determines the correct position of the blend air flaps and actuates them separately.

The selected temperature is reached and maintained as quickly as possible if warming or cooling of the interior is required.

Air distribution switch (4)

The air distribution switch (4) controls the air flow to the air outlets for ventilation of the passenger compartment.

The air distribution can be set manually by turning the air distribution switch (4).

By turning the air distribution switch (4) on the HEAT [HAU] control and operating unit (N18), the left blend air flap actuator motor, the right blend air flap actuator motor, the left and right footwell flaps actuator motor, the left and right defroster flaps actuator motor, and the fresh air flaps actuator motor are actuated via the AC bus. Apart from the 4 basic settings, additional 8 intermediate settings can be selected.

Defroster button (5)

Pressing the defroster button (5) initiates the defrost function.

The defroster function works according to the following new logic:

heating power is controlled by the outside temperature.
the entire air flow is directed towards the windshield and front side windows, defroster outlets opened
blend air flaps controlled
footwell vents closed
blower power at 80 %, can be manually controlled

Air recirculation switch (N18s2)

The air recirculation switch (N18s2) is used to operate the fresh air/air recirculation flap in order to enable air supply from the vehicle interior.

Briefly pressing the air recirculation switch (N18s2) for < 1.5 s actuates the fresh air/air recirculation flaps actuator motor which actuates the fresh air/air recirculation flap, which in turn closes the fresh air duct and opens the recirculated air duct to enable air to be supplied from the vehicle interior. The LED in the air recirculation switch (N18s2) is on during air recirculation mode.

Recirculation air convenience closing function

If the air recirculation switch (N18s2) is pressed for longer than 1.5 s, all open windows and the tilting/sliding roof (SHD) (with code (414) Power glass tilting/sliding roof) are closed in automatic mode (windows and tilting/sliding roof (SHD) must be normalized) in addition to activation of the recirculated air function. The LED in the air recirculation switch (N18s2) is on during air recirculation mode. The tilting/sliding roof (SHD) and the power windows are actuated subsequently to prevent current peaks.

If the button is pressed once again for > 1.5 s, the windows and the tilting/sliding roof (SHD) move back to the previously stored positions and the fresh air/air recirculation flap moves to the fresh air position (LED off).

The convenience closing function can only be started if the LED in the air recirculation switch (N18s2) is not illuminated.

Any window which has been opened manually during air recirculation mode remains in this position when the recirculation air function is canceled; all other windows move to the stored positions. The positions of the tilting/sliding roof (SHD) and of the windows prior to the commencement of the closing operation are stored by the overhead control panel control unit or by the door control units. The windows and the tilting/sliding roof (SHD) which were closed using the convenience locking function remain closed when the air recirculation switch (N18s2) is pressed for < 1.5 s. In this case only the fresh air/ recirculated air flap is moved into the fresh air position. The stored positions are canceled when the ignition is switched off.

REST button (with code (450) Taxi version or code (670) Residual engine heat utilization system (REST [MRA]))

When the REST button (which is combined with the air recirculation switch (N18s2)) is pressed, the residual engine heat utilization system is switched on. When the engine is switched off, the residual heat heats the vehicle interior as a function of the temperature set on the HEAT [HAU] control and operating unit (N18) and of the ambient temperature. The vehicle can be heated for approx. 30 minutes with the engine switched off. The function is only available when the ignition is switched off or when the transmitter key in the EIS [EZS] control unit is in position 1. The residual engine heat utilization system is switched off automatically in the event of undervoltage. The flaps for the air distribution and the air volume are regulated automatically.

The residual heat function is switched off under the following conditions:

Transmitter key in position 2
Approx. 30 min have elapsed
Battery voltage drop below 11 V