GF83.70-P-0006GM Stationary Heater (STH), Function
GF83.70-P-0006GM Stationary Heater (STH), Function
- with CODE (228) Stationary heater
General function requirements
^ Sufficient remaining quantity of fuel in tank
Stationary heater (STH), general
Before starting the trip the STH ensures:
- the interior compartment is preheated
- the windows are free of ice and condensation
- the engine is preheated
The use of the stationary heater reduces:
- the accident hazard by providing clear visibility 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 protect the environment by reducing the pollutants in the exhaust when starting up a preheated 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 the vehicle interior to below the outside temperature.
Heating or ventilation mode can be triggered in the following ways:
- immediately via the STH switch (N72/1s30) or STH radio remote control transmitter (A8/3)
- preprogrammed via the left multifunction steering wheel button group (S110) and right multifunction steering wheel button group (S111)
The main component is the STH heater unit (A6). The STH heater unit comprises all components necessary for generating and exchanging heat.
The STH heater unit is directly connected to the heating and cooling circuit of the vehicle engine. The auxiliary heater metering pump (M46/1) provides the fuel supply for the STH heater unit.
The STH is comprised of the following subfunctions:
^ Function sequence, teach-in of STH transmitter
^ Function sequence, trigger immediate heating mode with STH transmitter
^ Function sequence, trigger immediate heating mode with STH switch
^ Function sequence, programming of preselection time
^ Function sequence, trigger heater preselect mode
^ Function sequence, decide to heat or ventilate
^ Function sequence, heating mode
^ Function sequence, ventilation mode
^ Function sequence, component test
^ Function sequence, STH shutoff
Function sequence, teach-in of 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. For this purpose, the STH switch must be pressed for approx. t = 20 s until the red LED in the STH switch flashes on and off.
The actuation of the STH switch is read in by the upper control panel control unit (N72/1) and transmitted to the STH control unit (A6n1) via the interior CAN (CAN B). After the STH switch has been actuated for approx. t = 20 s, the STH control unit transmits feedback to the upper control panel control unit and the red LED in the STH switch is triggered to flash.
As soon as the red LED starts to flash, the STH switch must be released to open the teach-in period window. The request to open the teach-in period window is read in by the upper control panel control unit and transmitted to the STH control unit via interior CAN. This transmits the request to the STH receiver and the teach-in period window is opened for max. t = 5 s.
The "OFF" button on the STH transmitter must be pressed during this period. The signal is transmitted by the STH transmitter via radio to the roof antenna module (A2/93). From there, the signal is transmitted directly to the STH receiver or, with code (386) Mobile phone comfort telephony, directly to the telephone/cell phone/STH radio remote control antenna splitter (A2/53) and from there on to the STH receiver. The STH receiver saves 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 three STH transmitters. If an additional STH transmitter undergoes teach-in, then the STH transmitter that underwent teach-in first is deleted.
The teach-in period window can also be opened using the diagnostic tester. The various opening times can only be configured using the diagnostic tester, similarly the number of STH transmitters that have undergone teach-in are read out.
The radio signal path is bidirectional i.e. if a radio signal from the STH transmitter does not reach the STH receiver, this is indicated on the STH transmitter.
The range of the stationary heater transmitter is s = 300 m. External influences can reduce the range, for example:
- radio interference
- solid obstacles (e.g. enclosed premises)
- unfavorable position to the vehicle
Function sequence, trigger immediate heating mode with STH transmitter
If the "ON" button on the stationary heater transmitter is pressed, the switch-on signal is transmitted by radio. This is detected by the roof antenna module and transmitted directly to the STH receiver or, with code (386) Mobile phone comfort telephony, directly to the antenna splitter and then relayed to the STH receiver. The STH receiver transmits the switch-on signal to the STH control unit, which transmits the query "Ventilate or heat" via interior CAN t the AAC [KLA] control and operating unit (N22) (without code (581) Comfort automatic air conditioning) or to the comfort AAC control and operating unit (N22/7) (with code (581) Comfort automatic air conditioning).
The radio signal path is bidirectional i.e. if a radio signal does not reach the STH receiver, this is displayed on the STH transmitter.
The range of the stationary heater transmitter is s = 300 m. External influences can reduce the range, for example:
- radio interference
- solid obstacles (e.g. enclosed premises)
- unfavorable position to the vehicle
Function sequence, trigger immediate heating mode with STH switch
Triggering the immediate heating mode function sequence with the STH switch consists of the following subfunctions:
^ Function sequence, trigger immediate heating mode with circuit 15R Off
^ Function sequence, trigger immediate heating mode with circuit 15R On
Additional function requirements for triggering immediate heating mode with circuit 15R Off
^ Circuit 15R OFF
Terminal status c. 15 is provided by the EIS control unit (N73) to the interior CAN.
Function sequence, trigger immediate heating mode with circuit 15R Off
When the STH switch is actuated, the switch-on signal is read in by the upper control panel control unit and transmitted via interior CAN to the STH control unit, which transmits the query "Ventilate or heat" to the control and operating unit via interior CAN.
Additional function requirements for triggering immediate heating mode with circuit 15R On
^ Circuit 15R ON
Function sequence, trigger immediate heating mode with circuit 15R On
When the STH switch is actuated for t > 2 s, the switch-on signal is transmitted by the upper control panel control unit to the STH control unit via interior CAN. The STH control unit transmits the request "Ventilate or heat" via the interior CAN to the control and operating unit and also sends a request to the instrument cluster (A1) via the interior CAN to open the preselection time menu.
The preselection times are shown via the multifunction display (A1p13) of the instrument cluster.
When the STH switch is actuated for t < 2 s, only the preselection time menu is called up in the instrument cluster, the STH is not switched on.
Additional function requirements for programming preselection time
^ Circuit 15R ON
The preselection time corresponds to the desired starting time for the stationary heater (up to 30.6.09) or the desired shutdown time (as of 1.7.09).
Function sequence, programming of preselection time
The preselection time menu is called up in the instrument cluster via the multifunction steering wheel button groups. The request is transmitted via the steering LIN (LIN E1) to the steering column tube module (N80) and from there via the engine compartment CAN (CAN C) to the instrument cluster.
The preselection time is displayed on the multifunction display of the instrument cluster.
The preselection time menu can also be called up via the STH switch. When the STH switch is actuated for t < 2 s, the preselection time menu is called up but the STH is not switched on. At the same time the status of the STH switch is read in by the upper control panel control unit and transmitted to the STH control unit via the interior CAN. The STH control unit transmits a request to the instrument cluster to open the preselection time menu via interior CAN. The preselection time is then set using the multifunction steering wheel button groups and can be activated by selecting the corresponding preselection time.
The instrument cluster stores a maximum of three preselection times.
When the STH switch is actuated for t > 2 s, the preselection time menu in the instrument cluster is called up and the query Ventilate or heat" is transmitted to the control and operating unit.
Additional function requirements for triggering heater preselect mode
^ Circuit 15C OFF
^ Preselection time activated
Function sequence, trigger heater preselect mode
On vehicles up to 30.6.09
At the determined start time, the instrument cluster transmits the switch-on command to the STH control unit via interior CAN, which transmits the query "Ventilate or heat" to the control and operating unit via interior CAN. The STH control unit also transmits a signal to the upper control panel control unit via interior CAN and the yellow LED in the STH switch lights up. The yellow LED goes out after the STH is switched on.
The preselection time corresponds to the desired STH starting time.
The activation via a current preselection time is suppressed if heating mode has been switched on manually in the meantime.
For vehicles as of 1.7.09
After a preselection time has been activated, the instrument cluster calculates the time remaining until the preselection time based on the current time and activated preselection time. The STH control unit also transmits a signal to the UCP [OBF] control unit via interior CAN and the yellow LED in the STH switch lights up. The yellow LED goes out after the STH is switched on.
One hour before the entered preselection time, the instrument cluster transmits a query to the control and operating unit via interior CAN to determine the period of heating/ventilation that is actually required. Based on the current outside and interior temperature measurements, the control and operating unit determines the optimal duration of heating/ventilation.
The outside temperature is recorded by the outside temperature indicator temperature sensor (B14) and read directly by the control and operating unit. The interior temperature is measured by the in-car temperature sensor (N22b1) (without code (581) Comfort automatic air conditioning) or the in-car temperature sensor (N22/7b1) (with code (581) Comfort automatic air conditioning) in the control and operating unit. The duration of heating/ventilation is transmitted to the instrument cluster via interior CAN. The instrument cluster determines the switch-on time based on the preselection time and the required period of heating/ventilation. At the determined switch-on time, the instrument cluster transmits the switch-on command to the STH control unit via interior CAN, which transmits the query "Ventilate or heat" to the control and operating unit via interior CAN.
The preselection time corresponds to the desired departure time.
The activation via a current preselection time is suppressed if heating mode has been switched on manually in the meantime.
Function sequence, decide to heat or ventilate
The STH control unit transmits the query "Ventilate or heat" to the control and operating unit via interior CAN.
Based on the current outside and interior temperature measurements, the control and operating unit determines the optimal duration of heating/ventilation.
The outside temperature is recorded by the outside temperature indicator temperature sensor and read in directly by the control and operating unit.
The interior temperature is measured by the in-car temperature sensor in the AAC control and operating unit.
It then decides whether to "Ventilate or heat" depending on the values determined and the last setting of the control and operating unit.
The red LED in the STH switch lights up while the decision is being made. The LED is actuated from the STH control unit via the upper control panel control unit via interior CAN. After t = 2 s, the STH control unit is informed of the decision to "Ventilate or heat" via interior CAN and either heating or ventilation mode is switched on. The decision is indicated visually by the LED in the STH switch. The red LED indicates stationary heating, and the blue LED stationary ventilation. The LED is actuated as described above. The STH control unit also reports the corresponding status back to the STH transmitter.
The following messages may be displayed on the STH transmitter:
- "FAIL": No wireless connection or heater operation not possible (note corresponding symbol)
- "ON": STH activated
- "OFF": STH deactivated
When the STH is switched on, a query on the status of all components involved in the heating mode is conducted and a self- test is performed if required. The heating mode is not started in the event of a relevant fault. The stationary ventilation function however is always performed, irrespective of the result.
Function sequence, heating mode
After the decision to "Heat" is made, the STH control unit starts the heating mode. The combustion air blower (A6m2) is actuated and operates close to its highest speed. The glow pin of the flame monitor glow pin unit (A6r4) is switched on. The preglow time of approx. t = 30 s starts.
After the preglow time, the combustion air blower is switched off briefly and the auxiliary heater metering pump starts to pump fuel. The combustion air blower starts again and, like the auxiliary heater metering pump, increases its speed and output to full load within the next approx. t = 60 s.
The fuel and the combustion air form the fuel/air mixture in the combustor housing. Once the increase in the flow of combustion air and fuel delivery has been completed, the glow pin of the flame monitor glow pin unit is switched off, and the safety period begins for approx. t = 45 s to check the flame.
After the end of the safety period and during heating mode, the flame monitor glow pin unit reports the following statuses in its function as flame monitor:
- "hot" = sufficient combustion, heater operation continues.
- "cold" = no flame, flame-out or insufficient flame formation, the auxiliary heater metering pump is switched off.
On vehicles with gasoline engine, startup is repeated once. If there is still no flame formation, fuel supply is stopped by switching off the auxiliary heater metering pump and fault shutoff with combustion air blower run-on takes place.
The heater operation is controlled automatically depending on the coolant temperature. Possible operating states:
- Full load operation
- Partial load operation
- Control interval
The STH switchover valve (Y16) is closed at coolant temperatures T < 60 �C (small coolant circuit). As of T = 60 °C, it is pulse actuated by the STH control unit and the large coolant circuit is then also heated. The coolant circulation pump (M13) ensures that the temperature-controlled coolant is circulated in the coolant circuit. It is actuated directly by the control and operating unit. If the temperature is sufficient, the control and operating unit actuates the blower regulator (A32n1) via the climate control LIN (LIN B8). This actuates the blower motor (A32m1).
The stationary heater primarily heats up the vehicle interior. Heating of the engine coolant is a secondary function. If the engine is started during heating operation, the engine first heats up itself, then starts to heat the interior once the coolant temperature in the engine (large circuit) has exceeded the temperature of the heat exchanger (small circuit).
Depending on the interior temperature, a switchover from stationary heating to stationary ventilation and vice versa can be made.
Function sequence, ventilation mode
After the decision is made to "Ventilate", only the ventilation in the vehicle is switched on. The control and operating unit actuates the blower regulator via the climate control LIN, which then actuates the blower motor.
Depending on the interior temperature, a switchover from stationary ventilation to stationary heating and vice versa can be made.
Function sequence, component test
When the STH is switched on, a check is made to determine whether a component fault was stored during the previous heate operation (component status) or whether the STH heater unit is disabled due to fault or overheating.
If a relevant fault is found to be stored in the STH control unit, no start attempt is made and a component test is performed instead. If no faults are detected any more, the component status is set to OK for the next switch-on attempt
The following components are monitored for open circuit, short circuit and proper operation during startup and during heater operation:
- Temperature sensor (A6b1)
- Thermal fuse (A6f1)
- Circulation pump (A6m1)
- Fuel preheating system (A6r5) (with diesel engine)
- Combustion air blower
- Glow pin unit flame monitor
- Auxiliary heater metering pump
- STH switchover valve
If a fault is detected, the heater operation startup process or heater operation is only aborted if the faulty component is essential for operation.
This is not the case for the STH switchover valve, a fault with the STH switchover valve does not cause heater operation to be terminated. The STH switchover valve is thus not taken into account when assessing the component status.
The tank content is also checked during STH startup. The tank status is stored every time circuit 15 is switched off so that the information is available immediately upon startup. Heater operation is only started if there is enough fuel left in the tank.
Compliance with the tank reserve signal can be disabled using the diagnostic tester.
Function sequence, STH shutoff
The STH shut-off function sequence comprises the following subfunctions:
- Function sequence, terminate heating mode
- Function sequence, terminate ventilation mode
- Function sequence, shutoff due to overheating
- Function sequence, safety shutoff due to crash
Function sequence, terminate heating mode
Heating mode is automatically terminated by the STH control unit or it can be manually aborted early using the STH transmitter or STH switch. 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 t = 60 min using the diagnostic tester.
The combustion is terminated by switching the auxiliary heater metering pump off. The run-on time of the combustion air blower starts.
The run-on time and speed of the combustion air blower depend on the operating condition (full-load operation, partial load operation or control pause) from which the STH heater unit was switched off.
If the engine is started during heating mode, expiration of the heating time is ignored and the system continues to heat until the coolant temperature of the engine (large circuit) exceeds the temperature of the heat exchanger (small circuit) by T = 5 °C.
Function sequence, terminate ventilation mode
Ventilation mode is automatically terminated by the STH control unit or it can be manually aborted early using the STH transmitter or STH switch. With the basic setting, the maximum ventilation time is limited to t = 50 min, as is the heating time.
This can be changed in t = 10 min steps between t = 10 min and t = 60 min using the diagnostic tester.
A shortening factor can also be set using the diagnostic tester. The following shortening 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 STH heater unit, the thermal fuse detects overheating and triggers the heater unit fault run-on process for approx. t = 120 s followed by fault interlock. Operation after shutoff via the thermal fuse resumes:
- via the diagnostic tester or
- via temporary interruption of the power supply (e.g. fuse removal). To do this, the STH switch must first be operated for at least t = 5 s up to a maximum of t = 15 s. After releasing the STH switch, the fuse must be removed within t = 30 s to achieve a reset of the fault interlock.
Function sequence, safety shutoff due to crash
The restraint systems control unit (N2/7) transmits the crash signal via engine compartment CAN to the central gateway control unit (N93). The central gateway control unit forwards the signal via interior CAN to the STH control unit, which then switches off the STH heater unit permanently.
The shutoff process can only be reset using the diagnostic tester.
