Automatic Heater (HEAT) Function

GF83.25-P-0001P Automatic Heater (HEAT) Function

MODEL 203.0 /2 /7 up to 23.4.04
- except CODE (580) Air conditioning (or Tempmatic for USA)
- except CODE (580) Automatic air conditioning
- except CODE (581) Automatic air conditioning
- except CODE (581) Comfort automatic air conditioning

The automatic heater (HEAT) is equipped with an electronically controlled cooling, heating and ventilation system, and can be summarized under the subfunctions listed in the following.

Ventilation
Ventilation ensures aeration in the vehicle interior. Ventilation is achieved with the support of the blower motor (A32m1) during normal operation, when vehicle is stationary or to increase the air flow. The air is distributed in the vehicle interior via air distribution flaps.

In order to prevent the windows from fogging up, the footwell flaps are opened fully for approx. 30 s after the ignition has been switched on.

When switching off the ignition, the fresh air/recirculated air flap automatically moves to the 50 % fresh air and 50 % recirculated air position. This achieves a significant reduction in the flap closing forces.

Heating circuit
The coolant is heated by the engine and then routed through the heater heat exchanger. There, the heat is dissipated to the interior compartment air. Via the heater return, which contains the hot water recirculation pump (M13), the coolant is returned to the coolant pump.

The hot water recirculation pump (M13) ensures that the coolant is circulated. Coolant is always flowing through the heater heat exchanger. Control takes place separately for the left and right sides via the blend air flaps as a function of the desired interior temperature.

Automatic heater (HEAT [HAU]) control
The electronic control of the automatic heater (HEAT [HAU]) takes place via various control units which are interconnected over the Controller Area Network bus class B (interior) (CAN-B). The CAN-B is a bi-directional bus, i.e., each connected control unit receives and transmits information.

Automatic heater (HEAT [HAU]) temperature control
The desired interior temperature is achieved or maintained at a constant level by heating the air.
For more precise temperature control, the information of the outside temperature display temperature sensor and of the in-car temperature sensor are read in.

Residual engine heat utilization (with code (450) Taxi version or code (670) Residual engine heat utilization system (REST [MRA]))
Residual engine heat utilization enables the vehicle to be heated even when the ignition is OFF. To do this, the system uses the residual heat of the engine coolant.