"Controlled heater operation", function

W83.70-0017-09

1 Timer
2 Control module
3 Glow pin
4 Temperature sensor
5 Burner
6 Heat exchanger
7 Overheating sensor

V Combustion air
A Exhaust
KE Coolant inlet
KA Coolant outlet
KS Fuel

8 Coolant circulation pump
9 Burner housing
10 Flame sensor
11 Combustion air blower
12 Exhaust line with muffler
13 Combustion air line
14 Fuel metering pump
15 Automatic heater control panel

W83.70-0030-01

Heat output stages

P Power

G High

M Medium

K Low

A OFF

Heat output stages

P Power

G High

M Medium

K Low

A OFF

W83.70-0031-01

Temperature thresholds with engine standing still

T Temperature in Celsius

t time

GH Switch-on threshold for blower for vehicle heater

Temperature thresholds while driving

T Temperature in Celsius

t time

GH Switch-on threshold for blower for vehicle heater

Function sequence with engine standing still and while driving

 The auxiliary heater is switched on with the timer (1) for the auxiliary heater.

 The heater has completed the starting phase and is in the controlled shut-off phase.

 The blower for the vehicle heater is running. The temperature in the coolant circuit decreases.

 Coolant temperature with engine standing still  68°C:

Coolant temperature while driving  63°C:

- The heater starts up in the heat output stage "medium".

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 The temperature in the coolant circuit increases.

 Coolant temperature with engine standing still  79°C:

Coolant temperature while driving  74°C:

- The heater is switched to the heat output stage "low"

 The temperature in the coolant circuit continues to increase.

 Coolant temperature with engine standing still  85°C:

Coolant temperature while driving  80°C:

- The heater first switches to the cooling phase with shut-off delay and after termination of the delay switches to the controlled shut-off phase.

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Heat output stages for different heat dissipation rates

 When the heat dissipation remains at a constant low or medium rate the heater alternates between the "medium" heat output stage and the controlled shut-off phase.
During the controlled shut-off phase only the coolant circulation pump for the heater continues to run.

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 If the heat dissipation is higher the heater alternates from the "medium" heat output stage and the heat output stages "high" or "power".

 If the temperature in the coolant circuit does not decrease to below the switch-on threshold of 63 °C while driving, the heater remains in the controlled shut-off phase.

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Heat output stages

During controlled operation of the auxiliary heater the combustion air blower and fuel metering pump operate at different heat output stages depending on the coolant temperature.

 "Medium" stage

Coolant temperature  68°C  79°C

Combustion air blower = 3000 rpm

Fuel metering pump = 2.6 Hz

 "Low" stage

Coolant temperature > 79°C < 85°C

Combustion air blower = 1850 rpm

Fuel metering pump = 1 Hz

Other operating states

After termination of heating operation the heater always switches to a cooling phase with shut-off delay for cooling down and purging the heater. After expiration of this phase the heater switches to the controlled shut-off phase until the heating operation is started again.

 Cooling phase with shut-off delay

Coolant temperature > 85°C

Combustion air blower "Low" stage = 1850 rpm

Fuel metering pump = off

 Controlled shut-off phase

Coolant temperature > 68°C

Combustion air blower = off

Fuel metering pump = off

Coolant circulation pump = running