End heater operation, function

Function

The heater booster is automatically switched off by the extended-activity module (EAM) (N10/1), taking the following switch-off conditions into account.

Switch-off conditions:

- no voltage at circuit 15 (ignition OFF) or

- crash detected or

- overvoltage (16 V) or

- undervoltage (< 9 V) or

- heater level/relay energized (= implausible series connection)

When one of these switch-off conditions is detected, the heater element levels 1, 2 + 3 are switched off without delay. The Switch-on conditions OK signal in the extended-activity module (EAM) (N10/1) is reset and the main relay de-energized with a time delay (= 100 ms).

At Ignition OFF the time delay, with which the heater booster relay (K16/1) is switched off, is increased from 100 ms to 160 ms.

Additional switch-off conditions:

- blending air flap Position CLOSED
(= no heater output request) or

- Heater booster enable signal from the engine control unit (MSG) withdrawn

When one of these switch-off conditions is given, then first of all a switched on heater element level 1 is switched off.

If the heater element levels 2 + 3 are also switched on, then the extended-activity module (EAM) (N10/1) initiates the Switch off wait period (T2 = 0.5 s). After expiry of the Switch off wait period then the heater element levels 2 + 3 are also switched off.

Note:

A reset of the Heater booster enable signal by the engine control unit (ECU) does not cause the Switch-on conditions OK signal in the extended-activity module (EAM) (N10/1) to be modified.

The switch-off signal is regarded as valid by the engine control unit (ECU), when for 3 successive periods (30 ms) the valid frequency and the valid switch-off pulse duty factor (low-high level) are applied.