Heater overheated, 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 in partial load mode: The combustion is stable. The combustion air blower (A6m2) and the fuel metering pump (Y23) operate at the their lowest speed and capacity.

3 The coolant temperature in the heater increases to an impermissibly high temperature of 125 °C due to lack of or insufficient coolant flow.

4 The internal temperature sensor for the stationary heater/heater booster control module (A6n1) recognizes overheating and actuates a malfunction switch-off with subsequent malfunction lockout.

5 The fuel metering pump is switched off.

6 The actuation of the vehicle blower is interrupted and the blower is switched off.

7 The heater malfunction shut-off delay for cooling the heater and for purging the combustion chamber starts for approx. 110 s. The combustion air blower reduces its speed during the first 40 s of the shut-off delay to partial load operation and then increases again to almost full load operation.

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

9 The malfunction shut-off is terminated, the malfunction lockout is present. Restarting the heater is no longer possible.

 The malfunction lockout can be canceled after eliminating the malfunction by interrupting the power supply (circuit 30). For this purpose pull fuse 32 in fuse and relay box (F1) for approx. 10 s and reinsert.