Stationary heater (STH), function - GF83.70-P-0006CE
MODEL 204 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,
- High mechanical wear to 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:
- The interior is ventilated,
- Stored heat is reduced.
It is not possible to cool down below the outside temperature.
The following options for stationary heater operation are available:
- Immediately using the stationary heater button or the radio remote control transmitter
- Preprogrammed via the left multifunction steering wheel button group or the radio remote control transmitter
The heater unit is the main component in the STH.
This comprises all components necessary for generating and exchanging heat.
The heater unit is integrated directly into the engine's heating and cooling circuit and is supplied with fuel by the fuel pump.
The stationary heater enables the interior temperature to be increased to match the request.
These requests are dependent on the following temperatures being determined:
- Ambient temperature
- Interior temperature (in roof area)
- Interior temperature (in instrument panel area)
Outside temperature:
The outside temperature is recorded by the outside temperature sensor, whose signals are read in by the front SAM control unit. The front SAM control unit sends the temperature value over the interior CAN to the control and operating unit.
Interior temperature (in roof area),
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 reads in the signals of the interior temperature sensor directly and sends these over the interior CAN to the control and operating unit.
Interior temperature (in roof area),
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 reads in the signals of the interior temperature sensor directly.
Interior temperature (in instrument panel area):
The interior temperature is recorded by the interior temperature sensor.
The control and operating unit reads in the signals of the interior temperature sensor directly.
The stationary heater contains 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 transmits the circuit status circuit 15 via the interior CAN.
Function sequence for teaching in the radio remote control transmitter
Before the initial startup, the radio remote control receiver must "teach in" the radio remote control transmitter assigned to it.
The components have already been matched to each other at the factory. Teaching in again is only necessary upon exchange of the heater unit or the stationary heater control unit, 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 reads in the status of the stationary heater button directly and sends this over the instrument panel LIN, front SAM control unit and the interior CAN to the stationary heater control unit. The stationary heater control unit sends the request to open the teach-in period window, which is then opened for a maximum of t = 5 s, over a direct line to the radio remote control receiver.
The open teach-in window is indicated by the flashing 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 transmits a radio signal to the multifunction antenna.
The multifunction antenna routes the signal directly (without code (386) Comfort telephony) or over the antenna splitter (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.
The teach-in window can be opened using the diagnostic tester, whose time period can be configured and the number of radio remote control transmitters that have undergone teach-in can then be 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 routes it directly (without code (386) Comfort telephony) or over the 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 however reduce the range:
- 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 then sends a "Ventilate or heat" query over the 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:
Pressing one of the arrow buttons on the radio remote control transmitter causes the operating status of the stationary heater to be shown on 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 shows the corresponding 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 t = 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, if necessary, at the next switch-on attempt. The stationary ventilation function however is always performed, irrespective of the result.
In addition to the switchover valve, the following components of the heater unit are verified when starting and during heating mode for open circuit, short circuit and proper operation:
- Temperature sensor
- Temperature fuse
- Combustion air blower
- Glow plug/flame monitor unit
- Fuel preheating system heating element (for diesel engine)
- Fuel shutoff valve (for diesel engine)
- Fuel pump
A defect at the switchover valve does not result in interruption of the heating mode or its startup because this component is not relevant for the safe operation of the stationary heater.
The tank content is also checked during STH startup. To do so, when circuit 15 is switched off, the instrument cluster sends information on the fill level of the fuel tank over the chassis CAN, front SAM control unit and the interior CAN to the stationary heater control unit. The stationary heater control unit saves 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 has ended positively, the stationary heater control unit sends the "Ventilate" or "Heat" query over the interior CAN to the control and operating unit.
Whether heating or ventilation is required is determined by the control and operating unit through comparing the specified interior temperature to the actual interior temperature.
Depending on the values determined and the current setting on the control and operating unit, a decision is made to "Ventilate" or to "Heat".
After t = 2 s, the control and operating unit transmits 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, the front SAM control unit and the 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 circuit 15 status is sent by the electronic ignition lock control unit over the chassis CAN, front SAM control unit and the 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 is actuated.
Actuation of the blower motor occurs via the blower regulator.
At circuit 15 ON, the blower motor is actuated corresponding to the setting on the control and operating unit, so that the ventilation function moves to 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 for this and the glow pin of the glow plug/flame monitor unit is switched on. The preglow time of approx. t = 30 s starts.
After expiration of the preglow time, the fuel pump starts 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 is then formed.
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.
During the heating mode, the glow plug/flame monitor unit, in its function as flame monitor, reports:
- "Hot" = sufficient combustion, heater operation continues.
- "Cold" = no flame, flame-out or insufficient flame formation, the fuel pump is switched off and a repeat startup is initiated once. If there is still no flame formation, the fuel supply is stopped by switching off the fuel pump and a fault shutoff with combustion air blower run-on occurs.
The heater operation is controlled automatically depending on the coolant temperature. Possible statuses:
- Full load operation
- Partial load operation
- Control interval
Following the "Heat" decision, the control and operating unit transmits the request to switch on the coolant circulation pump over the interior CAN to the front SAM control unit. The front SAM control unit then directly actuates the coolant circulation pump. The temperature-controlled coolant is then circulated.
Parallel to this the control and operating unit actuates the blower motor through the blower regulator.
The stationary heater primarily heats the vehicle interior via the heat exchanger of the vehicle heating (small circuit).
If the coolant reaches a temperature of T = 40 °C, the blower motor is activated.
As of a coolant temperature of T = 60 °C, the switchover valve gradually activates the cooling circuit of the engine (large circuit) upon request by the stationary heater control unit.
Depending on the interior temperature, a switchover from stationary heating to stationary ventilation and vice versa can be made.
Upon reaching the departure time the stationary heater is switched on for t = 5 min. and then automatically switches off.
Function sequence for triggering immediate mode
The immediate mode can either be triggered via the stationary heater button or the radio remote control transmitter.
Triggering immediate mode with the radio remote control transmitter can be found in the subfunction "Operation with the radio remote control transmitter".
Pressing the stationary heater button activates the stationary heater.
The upper control panel control unit reads in the status of the stationary heater button directly and sends this over the instrument panel LIN, front SAM control unit and the interior CAN to the stationary heater control unit.
The stationary heater control unit sends the "Ventilate" or "Heat" query over the interior CAN to the control and operating unit. The stationary heater is activated in accordance with the feedback.
The further procedure is the same as for the "Ventilation or heating mode" subfunction.
Function sequence for programming the departure time and triggering ventilation/heating mode
The departure time can be programmed and activated via the menu "Settings" in the menu level "Heating" of the instrument cluster or via the radio remote control transmitter.
A maximum of three departure times can be programmed.
Activation of a corresponding departure time is signaled visually by the actuation of the yellow indicator lamp in the stationary heater button.
The stationary heater control unit sends the corresponding request over the interior CAN, front SAM control unit and instrument panel LIN to the upper control panel control unit, which then actuates the yellow indicator lamp in the stationary heater button.
The function sequence for programming the departure time and activating the ventilation/heating mode is made up of the following subfunctions:
- Function sequence for programming the departure time via the left multifunction steering wheel button group
- Function sequence for programming the departure time through the radio remote control transmitter
- Function sequence for triggering ventilation/heating mode for the departure time
Additional function requirements for programming the departure time via the multifunction steering wheel button groups
- Circuit 15R ON
The circuit 15R status is sent by the electronic ignition lock control unit over the interior CAN.
Function sequence for programming the departure time via the left multifunction steering wheel button group
The departure time menu is called up in the instrument cluster via the left multifunction steering wheel button group. The steering wheel electronics reads in the request directly and then sends it over the steering LIN, steering column tube module control unit and chassis CAN to the instrument cluster.
The departure time is displayed in the multifunction display (A1p13) of the instrument cluster. The departure time can then be configured and activated to match the menu navigation using the left multifunction steering wheel button group.
If a departure time was activated, the instrument cluster transmits the selected departure time via the interior CAN to the stationary heater control unit. The stationary heater control unit stores the departure time and reports this back to the instrument cluster, which also stores the selected departure time.
Function sequence for programming the departure time through the radio remote control transmitter
Alternatively, the departure time can be configured and activated using the radio remote control transmitter.
Set the departure time using the left or right arrow button and activate by pressing the "ON" button.
The radio remote control transmitter then transmits a radio signal to the multifunction antenna.
The multifunction antenna routes the signal directly (without code (386) Comfort telephony) or over the antenna splitter (with code (386) Comfort telephony) to the radio remote control receiver.
The radio remote control receiver transmits the departure time as a switch signal to the stationary heater control unit.
The stationary heater control unit then transmits the departure time via interior CAN to the instrument cluster, which stores the selected departure time. The stationary heater control unit then also stores the selected departure time.
Additional function requirements for triggering ventilation/ heating mode for the departure time
- Circuit 15C OFF, exception: Between the activation of the departure time and the switching on of the stationary heater, circuit 15C was constantly on.
- Activated departure time
The circuit 15C status is sent by the electronic ignition lock control unit over the interior CAN.
Function sequence for triggering ventilation/heating mode for the departure time
The instrument cluster queries the required ventilation/heating duration for the desired specified temperature from the control and operating unit approx. t = 60 min. before the desired departure time.
To do so, the instrument cluster transmits a corresponding query over the interior CAN to the control and operating unit.
The control and operating unit then determines the values of the following variables:
- Ambient temperature
- Interior temperature (in roof area)
- Interior temperature (in instrument panel area)
The control and operating unit uses the measured temperature values to determine the difference between the specified and actual value. The control and operating unit then calculates the required heating/ventilation duration in order to adjust the actual temperature to the specified temperature. The control and operating unit then sends this value over the interior CAN to the instrument cluster.
The instrument cluster uses the heating/ventilation duration and the current time to calculate the switch-on time.
Once the switch-on time is reached, the instrument cluster transmits the request to switch on the stationary heater to the stationary heater control unit. The stationary heater control unit then transmits the query "Heat" or "Ventilate" over the interior CAN to the control and operating unit.
The stationary heater is activated in accordance with the feedback from the control and operating unit and the yellow indicator lamp is deactivated.
A switch-on signal sent by the instrument cluster due to an activated departure time is suppressed if the ventilation/heating mode was triggered manually in the meantime.
The further procedure is the same as for the "Ventilation or heating mode" subfunction.
Function sequence, STH shutoff
The function sequence for shutting off the stationary heater encompasses the following subfunctions:
- Function sequence, terminate heating mode
- Function sequence, terminate ventilation mode
- Function sequence, shutoff due to overheating
- Function sequence for consumer shutoff in the event of undervoltage
- Function sequence, safety shutoff due to crash
Function sequence, terminate heating mode
The heat mode is terminated automatically by the stationary heater control unit or it can be manually aborted in advance using the radio remote control transmitter or the stationary heater button. With the basic setting, the maximum heating time is t = 50 min. This can be changed in t = 10 min steps between t = 10 min and 60 min using the diagnostic tester. Combustion is terminated by switching off the fuel pump.
If the engine is started during heating mode, expiration of the heating time is ignored and heating continues until the coolant temperature difference of the engine (large circuit) to the temperature of the coolant at the heater unit's coolant outlet is maximum T = 5 °C.
Function sequence, terminate ventilation mode
The ventilation mode is terminated automatically by the stationary heater control unit or it can be manually aborted in advance using the radio remote control transmitter or the stationary heater button. With the basic setting, the maximum ventilation time is t = 50 min. This can be changed in t = 10 min steps between t = 10 min and 60 min using the diagnostic tester.
In addition to this, a reduction factor can be configured using the diagnostic tester.
The following reduction factors can be set:
- Factor 1: ventilation time = 3/4 heating time
- Factor 2: ventilation time = 1/2 heating time
- Factor 3: ventilation time = 1/4 heating time
Function sequence, shutoff due to overheating
If the temperature of T = 125 °C is exceeded in the heater unit, the thermal fuse recognizes overheating via the temperature sensor and switches the stationary heater off with subsequent overheating locking.
After being switched off startup takes place:
- via the diagnostic tester or
- via temporary interruption of the power supply (e.g. electrical fuse 75 (N10/2f75) removal).
For safety reasons proceed as follows here:
- Press stationary heater button for at least t = 5 to 15 s.
- Remove fuse within t = 30 s.
- Reinsert fuse.
Function sequence for consumer shutoff in the event of undervoltage
To prevent battery discharging, the state of charge in the on-board electrical system is constantly evaluated by the stationary heater control unit.
The following undervoltage limits are valid for operation of the stationary heater:
- Gasoline engine: U = 11.3 V
- Diesel engine: U = 11.5 V
If the voltage drops below the listed voltage values for t > 20 s, the stationary heater control unit switches off the stationary heater.
Function sequence, safety shutoff due to crash
In the event of an accident, the supplemental restraint system control unit sends a request to switch off over the chassis CAN, front SAM control unit and the interior CAN to the stationary heater control unit. The stationary heater control unit then permanently switches off the stationary heater. The stationary heater can then only be started again using the diagnostic tester.
| Electrical function schematic, teach-in of stationary heater radio remote control transmitter | PE83.70-P-2052-97FAA | |
| Electrical function schematic, trigger immediate mode | PE83.70-P-2059-97FAA | |
| Electrical function schematic, programming departure time | PE83.70-P-2057-97FAA | |
| Electrical function schematic, trigger heating mode for departure time | PE83.70-P-2058-97FAA | |
| Overview of system components for stationary heater (STH) | GF83.70-P-9996CE |