Defect in engine coolant temperature measurement while heater is operated, function

P83.70-0393-09

1 Burner housing

2 Heat exchanger

3 Heater circuit thermostat

A6m1 Coolant circulation pump

Y23 Fuel metering pump

B Thermostat setting, open auxiliary circuit

A6m2 Combustion air blower

A6n1 Stationary heater/heater booster control module

N34 Stationary heater timer

Function sequence

1 Coolant temperature:> 59 °C :
The thermostat (3) is switched to heating mode, the stationary heater auxiliary circuit is connected to the cooling and heater circuit of the vehicle.

2 The heater operates at partial load or full load mode. The coolant circulation pump (A6m1) pumps coolant through the heat exchanger (2). The combustion air blower (A6m2) and the fuel metering pump (Y23) operate at partial load or full load speed and capacity.

3 The coolant temperature sensing is permanently monitored internally by the stationary heater control module (A6n1).

4 The control module recognizes a malfunction in the coolant temperature sensing:

 The temperature signal exceeds the temperature sensing range.

5 The control module starts a malfunction switch-off to protect the heater.

6 The fuel metering pump (Y23) switches off thereby interrupting the combustion in the burner housing (1).

7 The heater malfunction shut-off delay for cooling the heater and for purging the combustion chamber starts for approx. 110 s.

8 The heater shut-off delay is terminated. The combustion air blower (A6m2) and the coolant circulation pump (A6m1) switch off.

 To reset switch heater on and off again after eliminating the cause of the malfunction.