Stationary heater (STH), function - GF83.70-P-0006SX
MODEL 221.0 /1, 216.3 with CODE (228) Stationary heater up to Model Year 8
General information
Prior to starting a journey during the cold season the stationary heater (SH) ensures that:
- the passenger compartment is preheated,
- the windows are free of ice and condensation,
- the engine is preheated.
The use of the stationary heater reduces:
- the risk of an accident by providing excellent vision before starting out on a trip,
- the mechanical wear to the automotive engine associated with a cold start,
- fuel consumption and at the same time it also helps to preserve environmental resources by cutting down the pollutants in exhaust emissions when starting up a previously heated engine.
The stationary heater also comprises the stationary ventilation function.
This provides for the following at high ambient temperatures and a high interior temperature due to intense solar radiation:
- the interior is ventilated,
- stored heat is reduced.
It is not possible to cool down to below the outside temperature however.
The main component is the STH or HB heater unit (A6) on model 221 or the STH control unit (A6) on model 216. The heater unit contains all the components required for generating and exchanging heat.
The heater unit is connected directly to the heater and cooling circuits of the automotive engine and utilizes them to transmit heat via its circulation pump (M13).
The heater unit's fuel supply takes place via the STH or AUH fuel metering pump (Y23) on model 221 or the STH fuel metering pump (Y23) on model 216.
To enable the interior to be heated up faster, the heater unit regulates the flow of coolant depending on the temperature between the small and large coolant circuit via the STH switchover valve (Y16).
Possible activation modes
The heater operation or stationary ventilation can
- be preprogrammed via the instrument cluster (A1) or
- switched on using the STH radio remote control transmitter (A8/3) or
- with the STH/HB [ZUH]/residual heat button (N72/1s30) on model 221 or the STH/residual heat button (N72/1s30) on model 216.
In the instrument cluster up to three preselected times can be stored, of which only one can be activated. The COMAND display (A40/8) serves here as a display instrument.
End heater operation or stationary ventilation
The functions are automatically ended by the stationary heater itself or can be manually canceled in advance using the stationary heater transmitter or the STH button.
Switchover between stationary heater and stationary ventilation
The stationary heater can correct the heating or ventilation choice as often as required. Depending on the temperature behavior, it can also change between ventilation and heating.
Component test
Prior to starting the heater operation, the status of all involved components is queried and a self-test performed where required. The heater operation is not started in the event of a relevant fault. However, the stationary ventilation function is always performed, irrespective of the result.
On model 216 and model 221 as of 1.6.06, the stationary heater status is shown on the stationary heater transmitter's display.
Engine start during heater operation
The stationary heater primarily heats up the vehicle interior. Heating of the engine coolant is secondary. If the engine is started during stationary heater operation, then the engine initially heats itself and only starts to heat the interior when the coolant temperature in the automotive engine (large circuit) exceeds the temperature of the heat exchanger (small circuit).
Heater booster function when driving (with diesel engine)
If the engine heat output is insufficient to heat the vehicle interior while driving, the heater unit is automatically activated for heating. At a coolant temperature of 82 °C the heater booster function automatically switches off and if the temperature drops to 72 °C, it switches on again automatically insofar as the requested interior temperature requires heater booster operation.
Consumer shutoff by vehicle power supply control unit (N82/1)
To prevent the battery from being discharged, the state of charge in the on-board electrical system is continuously evaluated. If a specific voltage value is dropped below, the vehicle power supply control unit switches off any consumers that require large currents until the state of charge is again acceptable. The also applies for the stationary heater.
Safety shutoff in the event of crash
If a crash signal is sent by the restraint systems control unit (N2/7) to the interior CAN, then the heater unit is permanently switched off. The shutoff process can only be reset using STAR DIAGNOSIS.
Teach-in of the STH transmitter
Before initial startup the STH radio remote control receiver (A6/1) must undergo a "teach-in" of the STH transmitters allocated to it. To do so, the STH button must be operated for approx. 20 s until the red indicator lamp flashes. After releasing the STH button, the teach-in period window is opened for a max. of 5 s.
The STH receiver notes the first, valid transmission signal it receives as the signal from the STH transmitter allocated to it. Following this, it then closes the teach-in period window and it has to be opened again to teach in another STH transmitter. The STH receiver can store up to 3 STH transmitters. If an additional STH transmitter undergoes teach-in, then the STH transmitter that underwent teach-in first is deleted.
The teach-in window can also be opened using STAR DIAGNOSIS. The various opening times can only be configured using STAR DIAGNOSIS, similarly the number of STH transmitters that have undergone teach-in are read out.
| Stationary heater (STH), location of components | GF83.70-P-0006-01SX |
| Stationary heater (STH) block diagram | GF83.70-P-0006-04SX |
| Component test function | GF83.70-P-3010SX |
| Activate heater immediately with radio remote control, function | GF83.70-P-3057SX |
| Activate preprogrammed heater, function | GF83.70-P-3058SX |
| Activate heater with stationary heater switch, function | GF83.70-P-3066SX |