Part 1

GF83.70-P-0006FQ Stationary Heater (STH), Function
MODEL 218
- with CODE (228) Stationary heater

Stationary heater (STH), general
In cold seasons before commencing a journey, the stationary heater ensures:
- 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 high mechanical wear of the 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 contains the stationary ventilation function.
This provides for the following at high ambient temperatures and a high interior temperature due to intense solar radiation:
- through-ventilation of the interior,
- store heat is reduced.
It is not possible to reduce the temperature below the outside temperature.
The following options for the operation of the stationary heater are available:
- Immediately using the stationary heater button (N72/1s30) or the stationary heater radio remote control transmitter (A8/3)
- Preprogrammed via the left multifunction steering wheel button group (S110) or the radio remote control transmitter
The central component of the stationary heater is the stationary heater unit (A6).
This comprises all components necessary for generating and exchanging heat.
The heater is directly integrated into the heating and cooling circuit of the engine and is supplied with fuel by the stationary heater fuel pump (Y23).
The stationary heater thus enables increasing or reducing the interior temperature of the vehicle in accordance with the operator's request.
These requirements are necessary for determining the following temperatures:
- Ambient temperature
- Interior temperature in the area of the roof
- Interior temperature in the area of the instrument panel
Outside temperature:
The outside temperature is recorded by the outside temperature sensor (B14), the signals of which are read in by the front SAM control unit with fuse and relay module (N10/1). The front SAM control unit sends the temperature value via interior CAN (CAN B) to the automatic climate control control and operating unit (N22/7).
Interior temperature in the area of the roof, On vehicles with code (414) Power glass tilting/sliding roof
The interior temperature is measured by the interior temperature sensor with integrated fan (N70b1).
The overhead control panel control unit (N70) reads in the signals of the interior temperature sensor directly and sends these via interior CAN to the control and operating unit.
Interior temperature in the area of the roof, On vehicles without code (414) Power glass tilting/sliding roof
The interior temperature is measured by the interior temperature sensor with integrated fan (N70/3b1).
The control and operating unit directly reads in the signals of the interior temperature sensor.
Interior temperature in the area of the instrument panel:
The interior temperature is recorded by the interior temperature sensor (B10/4).
The control and operating unit directly reads in the signals of the interior temperature sensor.
The stationary heater comprises the following subfunctions:
^ Function sequence for teaching in the radio remote control transmitter
^ Function sequence for operation with the radio remote control transmitter
^ Function sequence for checking the component status
^ Function sequence for activating ventilation or heating
^ Function sequence for ventilation or heating mode
^ Function sequence for triggering immediate mode
^ Function sequence for programming the departure time and triggering ventilation/heating mode
^ Function sequence, STH shutoff

Additional function requirements for teaching in the radio remote control transmitter
^ Circuit 30 ON or
^ Circuit 15C ON
The electronic ignition lock control unit (N73) sends the status of circuit 15 via interior CAN.

Function sequence for teaching in the radio remote control transmitter
Before initial start-up, the stationary heater radio remote control receiver (A6/1) must "learn" the radio remote control transmitters assigned to it.
The components are already matched at the factory. Teaching in again is only necessary upon exchange of the heater or the stationary heater control unit (A6n1), the radio remote control receiver or the radio remote control transmitter.
The stationary heater button must be pressed for approx. t = 20 s for this. The upper control panel control unit (N72/1) reads in the status of the stationary heater button directly and sends this via the instrument panel LIN (LIN 1), front SAM control unit and interior CAN to the stationary heater control unit. The stationary heater control unit sends the request to the radio remote control receiver via direct line to open the teach-in period window, which is then opened for maximum t = 5 s.
The open teach-in window is signaled by the flashing of the red indicator lamp in the stationary heater button.
Now the "OFF" button must be pressed within the open teach-in window for at least t = 1 s until the display shows "OFF". The radio remote control transmitter then sends a radio signal to the multifunction antenna (A28/11).
The multifunction antenna forwards the signal via a direct line (without code (386) Comfort telephony) or via the mobile phone and stationary heater radio remote control antenna splitter (A2/53) (with code (386) Comfort telephony) to the radio remote control receiver.
The radio remote control receiver saves the first valid transmission signal it receives as the signal from the radio remote control transmitter assigned to it. Following this, the teach-in period window closes and must be opened again to teach in another radio remote control transmitter.
The radio remote control receiver can store up to three radio remote control transmitters. If an additional radio remote control transmitter is taught in, the first radio remote control transmitter that was taught in is deleted.
Using the diagnostic tester, the teach-in period window is opened, its time period set and the number of taught-in radio remote control transmitters read out.

Function sequence for operation with the radio remote control transmitter
If the "ON" button on the radio remote control transmitter is pressed, the switch-on signal is broadcast by radio.
The multifunction antenna records this radio signal and forwards it via a direct line (without code (386) Comfort telephony) or via the mobile phone and stationary heater radio remote control antenna splitter (with code (386) Comfort telephony) to the radio remote control receiver.
The range of the radio remote control transmitter is maximum s = 300 m (outdoors).
External influences can reduce the range, however:
- radio interference
- solid obstacles (e.g. enclosed premises)
- unfavorable position to the vehicle
The radio remote control receiver sends the switch-on signal to the stationary heater control unit, which sends a "Ventilate or heat" query via interior CAN to the control and operating unit.
The stationary heater is then activated accordingly.
Based on the status information present, the stationary heater control unit reports the status of the stationary heater back to the radio remote control transmitter over the reverse path.
The radio signal path is bidirectional, i.e. if the radio signal does not reach the radio remote control receiver, this is displayed at the radio remote control transmitter.
In the course of operation of the stationary heater, the stationary heater control unit constantly reports back the status at the radio remote control receiver so that the user can query the status of the stationary heater at any time.
The departure times can be called up, set, activated or deactivated.
The corresponding user requests are stored in the stationary heater control unit.
The following operation options result from this individually and require trouble-free communication with the stationary heater control unit:
- Triggering immediate mode
- Calling up a departure time
- Setting a departure time
- Activating a departure time
- Deactivating a departure time
- Querying operating condition of STH
Triggering immediate mode:
The ventilation or heating mode that corresponds to the temperature relationship is triggered by pressing the "ON" button once.
Calling up a departure time:
By pressing one of the arrow buttons once on the radio remote control transmitter, the operating condition of the stationary heater is shown in the display. By pressing the "right" arrow button again, the first of three possible departure times is shown, if programmed.
Pressing this again shows the second departure time and pressing a third time correspondingly shows the third departure time. Upon request, the departure times are only shown in the radio remote control transmitter, not stored.
Setting a departure time:
To call up the setting mode, the buttons "ON" and "OFF" must be pressed at the same time within t < 0.7 s.
With the setting mode activated, the clock symbol in the display flashes. Setting is performed via the arrow buttons. To adopt the newly set time, the buttons "ON" and "OFF" must again be pressed again at the same time within t < 0.7 s.
Activating a departure time:
To activate a departure time, the "ON" button must be pressed after calling up the desired time.
Deactivating a departure time:
To deactivate a departure time, the desired departure time must be called up and then the "OFF" button pressed. Following deactivation, the display of the radio remote control transmitter shows the operating condition of the stationary heater.
Querying the operating condition of the stationary heater:
By pressing one of the arrow buttons on the radio remote control transmitter once, the operating condition can be queried at any time irrespective of the manner in which the stationary heater was activated.
The status of the stationary heater is shown in the display of the radio remote control transmitter in accordance with the operating condition.
The possible indications in the display of the radio remote control transmitter can be found in the separate description "Stationary heater radio remote control transmitter, component description".
The duration for which these messages are displayed can be set in the stationary heater control unit using the diagnostic tester in steps of 2 seconds within a range of t = 4 s and 30 s.

Function sequence for checking the component status
When activating the stationary heater, first the status if all components participating in the heating mode is queried. If the status "Fault present" is determined, no switch-on attempt is initialized and the component fault is verified by a self-test. The result of this test updates the status so that - depending on the result - heating is possible again upon the next switch-on attempt, if necessary. The stationary ventilation function however is always performed, irrespective of the result.
In addition to the stationary heater switchover valve (Y13), the following components of the heater are checked when starting and during heating mode for open circuit, short circuit and proper operation:
- Stationary heater temperature sensor (A6b1)
- Stationary heater thermal fuse (A6f1)
- Stationary heater combustion air blower (A6m2)
- Stationary heater glow plug/flame monitor unit (A6r4)
- Stationary heater fuel preheater heating element (A6r5) (with diesel engine)
- Stationary heater fuel shutoff valve (A6y2) (with diesel engine)
- Fuel pump
A defect of the switchover valve does not result in interruption of the heating mode or its start-up because this component is not relevant for the safe operation of the stationary heater.
The tank content is also checked during STH start-up.
To do so, the instrument cluster (A1) sends information on the fill level of the fuel tank via chassis CAN (CAN E), front SAM control unit and interior CAN to the stationary heater control unit upon switching off circuit 15. The stationary heater control unit stores the information on the fill level of the fuel tank. Heating mode is only started if the remaining amount of fuel is greater than the tank reserve (minimum tank fill level).

Function sequence for activating ventilation or heating
After the component status query was ended positively, the stationary heater control unit sends the "Ventilate or heat" query via interior CAN to the control and operating unit.
Whether heating or ventilation is required is determined by the control and operating unit by means of the comparison of the specified to the actual interior temperature.
Depending on the values determined and the current setting at the control and operating unit, this then decides whether to "Ventilate or heat".
After t = 2 s, the control and operating unit sends the "Ventilate or heat" request via interior CAN to the stationary heater control unit, which implements this accordingly.
This activity is signaled by the red indicator lamp in the stationary heater button lighting up.
The indicator lamp is actuated by the stationary heater control unit via interior CAN, front SAM control unit and instrument panel LIN by the upper control panel control unit.
The current operating condition is signaled as follows:
- Indicator lamp red: stationary heating
- Indicator lamp blue: stationary ventilation

Additional function requirements for ventilation or heating mode
^ Circuit 15 OFF (valid for ventilation mode)
The electronic ignition lock control unit sends the status of circuit 15 via chassis CAN, front SAM control unit and interior CAN to the control and operating unit.

Function sequence for ventilation or heating mode
In accordance with the "Ventilation" request from the control and operating unit, only the blower motor (A32m1) is actuated.
The blower motor is actuated via the blower regulator (A32n1).
With circuit 15 ON, the blower motor is actuated in accordance with the setting selected at the control and operating unit such that the ventilation function retreats into the background. The Indicator lamp in the stationary heater button lights up blue.
If the "Heat" request results from the specified/actual comparison of the outer and interior temperature, the stationary heater control unit starts the heating mode.
The combustion air blower is actuated by the stationary heater control unit and the glow pin of the glow plug/flame monitor unit is switched on. The preglow time of approx. t = 30 s starts.
After the expiration of the preglow time, the fuel pump begins delivering fuel.
The fuel that evaporates on a non-woven metal fabric of the burner housing forms a fuel/air mixture together with the combustion air.
This fuel/air mixture is ignited by the glow plug; a flame forms.
The function of the glow plug then transitions into the function of the flame monitor. The combustion air blower and the fuel pump increase the rotational speed and the output to wide open throttle within the next approx. t = 60 s.