"Start heater operation, warm start", 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

W83.70-0026-01

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

W83.70-0027-01

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

 Auxiliary heater switched on with timer (1) for auxiliary heater. Heater has completed the cold start sequence up to reaching the maximum temperature in the coolant circuit and the cooling phase with shut-off delay has been completed. The temperature in the cooling circuit has decreased to 68 °C. The coolant circulation pump is running. The blower for the vehicle heater is running.

 The combustion air blower (11) and glow pin (3) are switched on.

 The combustion air blower runs for 5 seconds at 3000 rpm and the speed is then reduced to 300 rpm. After 55 seconds the speed of the combustion air blower is increased again linearly up to the "medium" heat output stage in which it runs at 3000 rpm.

 Parallel to this the fuel metering pump (14) is started at a frequency of 2.6 Hz after 40 seconds, after running for
15 seconds the pumping rate is released to 1 Hz and then increased linearly after 65 seconds to 2.6 Hz in the "medium" heat output stage. The fuel/air mixture is then formed and ignited on the glow pin.

 After 85 seconds the glow pin is switched off.

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 The control module checks whether flame is present in the burner with the aid of the flame monitor (10).

- If combustion has stabilized:
The starting sequence is continued.

- If flame formation is not sufficient:
The control module attempts to start up the heater a second time.

 The coolant is heated in the heat exchanger and the coolant temperature increases. The heater then continues to operate in the "medium" heat output stage until the coolant temperature has reached the first temperature threshold.

 The control module switches the heater to the "low" heat output stage.

 Upon exceeding the maximum temperature the control module switches the heater to the cooling phase with shut-off delay:

- Then the fuel metering pump is switched off immediately.

- The combustion air blower continues to run for
210 seconds and is then switched off.

- The coolant circulation pump and blower for the vehicle heater remain on continuously until the timer is switched off manually.

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Temperature thresholds with engine standing still:

 Coolant temperature  68°C:

The heater is switched to "medium" heat output stage upon reaching a temperature threshold of 79°C.

 Coolant temperature  79°C:
The heater is switched to "low" heat output stage upon reaching a temperature threshold of 85 °C.

 Coolant temperature  85°C:
The heater is switched to the cooling phase with shut-off delay:

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Temperature thresholds while driving:

 Coolant temperature  63°C:

The heater is switched to "medium" heat output stage upon reaching a temperature threshold of 79°C.

 Coolant temperature  74°C:
The heater is switched to "low" heat output stage upon reaching a temperature threshold of 85 °C.

 Coolant temperature  80°C:
The heater is switched to the cooling phase with shut-off delay:

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Heat output stages with engine standing still

During the starting operation for the auxiliary heater the combustion air blower and fuel metering pump are operated at various 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

Operating state upon exceeding maximum temperature

 Cooling phase with shut-off delay

Coolant temperature > 85°C

Combustion air blower, low stage = 1850 rpm

Fuel metering pump = aus

Heat output stages while driving

During the starting operation for the auxiliary heater the combustion air blower and fuel metering pump are operated at various heat output stages depending on the coolant temperature.

 "Medium" stage

Coolant temperature > 63°C < 74°C

Combustion air blower = 3000 rpm

Fuel metering pump = 2.6 Hz

 "Low" stage

Coolant temperature > 74°C < 80°C

Combustion air blower = 1850 rpm

Fuel metering pump = 1 Hz

Operating state upon exceeding maximum temperature

 Cooling phase with shut-off delay

Coolant temperature > 80°C

Combustion air blower, low stage = 1850 rpm

Fuel metering pump = aus