Start heater operation, function

L83.70-0012-06

1 Water jacket

2 Coolant inlet

3 Coolant outlet

4 Heat exchanger

5 Combustor with downpipe

6 Main wiring harness connector to stationary heater

7 Stationary heater connector in electric box

8 Coolant circulation pump connector to stationary heater

A6 Stationary heater (STH)

A6m1 Combustion air blower

A6n1 Stationary heater control module

A6r1 Glow pin

A6r2 Overheating sensor for NTC resistor

A6r3 Temperature sensor for NTC resistor

A6r4 Flame sensor for PTC resistor

M46/1 Stationary heater fuel metering pump

Operational sequence

1 The stationary heater (A6) is switched on via the STH timer (N34) by switching on directly or by 3 programmable preselect times. As Special equipment it is possible to switch on the stationary heater via radio remote control (A8/3). A signal is transmitted from the timer (N34) or the radio remote control (A8/3) to the STH control module (A5n1).

When switching on the stationary heater, a stationary heater symbol appears in the display of the STH timer (N34).

2 The combustion air blower (A6m1) in the heater and the coolant circulation pump (M13/2) are activated from the STH control module (A6n1) and start to run. The combustion air blower (A6m1) pumps at its highest capacity in stage "LARGE".

3 The STH control module (A6n1) switches on the heater fan (M2) to stage 1, at a coolant temperature > 30 °C.

The heater fan (M2) is switched on via the air conditioning controls (N20) for vehicles with tempmatic air conditioning, or via the blower motor series resistor group (R13) for vehicles without tempmatic air conditioning.

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The temperature signal for switching on the heater fan (M2) is transmitted from the temperature sensor (A6r3) to the STH control module (A6n1).

4 In the STH control module (A6n1) the inquiry of the flame sensor (A6r4) is started. The flame sensor signals:

"cold" = no flame, start is continued,

"hot" = flame, start is aborted due to a temperature sensor (A6r3) defect (malfunction shutoff).
If "cold" is signaled within 300 s, start is continued.

5 The preheating time of approx. 45 s starts. The glow pin (A6r1) is switched on.

6 If the preheating time has ended, the STH fuel metering pump (M46/1) pumps the fuel. The fuel and the combustion air form the fuel/air mixture in the combustor housing.

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7 The safety time (approx. 90 s) for flame formation commences. The fuel/air mixture is ignited by the glow pin (A6r1), the flame sensor (A6r4) monitors the incipient combustion.

8 If the safety time is over, the flame sensor signals

"hot" = sufficient flame formed, the glow pin (A6r1) is switched off as a function of time.

"cold" = no flame formed or insufficient flame, the fuel metering pump (M46/1) is switched off and a one-off repeated start is initiated.

9 The fuel metering pump (M46/1) and the combustion air blower (A6m1) are switched to stage "SMALL" or "LARGE" (depending on the value of the temperature sensor (A6r3)) via the STH control module (A6n1)

 At the start, the coolant temperature must be below 70 °C. For the heater D 5W (diesel), in the run-on period after-glowing continues for a certain period of time (approx. 20 s). This
after-glowing prevents white smoke during combustion.