Stationary heater (STH), function - GF83.70-P-0006FL

MODEL 212 with CODE 228 (Auxiliary heater) 

Fig 1: Stationary Heater Block Diagram - Model 212 With Code 228 (Auxiliary Heater)

Courtesy of MERCEDES-BENZ USA

Stationary heater (STH), general 

The stationary heater can be operated in ventilation or heating mode and thus ensures a climate-controlled vehicle interior and that the windows are clear of ice and fogging before the vehicle is driven. Operating the stationary heater thus reduces the accident hazard by ensuring clear visibility when setting off.

The stationary heater can be switched on as follows:

• Immediately using the stationary heater button or the radio remote control transmitter
• Preprogrammed by activating a time of departure

The radio remote control receiver saves the current operating status for the stationary heater. The stationary heater control unit continuously sends information on the stationary heater's operating condition to the radio remote control receiver, which can be queried via the radio remote control transmitter. This information is only provided in response to a request via the radio remote control transmitter.

The heater unit is the main component in the STH. It contains all components necessary to generate heat. The heater unit is connected to the engine's coolant circuit and is supplied with fuel by the stationary heater fuel pump.

For stationary heater operation, the following temperatures must be determined:

• Outside temperature: 

  The outside temperature is recorded by the outside temperature sensor. The front SAM control unit reads in the outside temperature sensor signal directly, calculates the outside temperature and sends this via interior CAN to the AAC control and operating unit.

• Interior temperature in roof area, in vehicles with CODE 414 (Power glass tilting/sliding roof): 

  The interior temperature in the area of the roof is measured by interior temperature sensor. The overhead control panel control unit reads in the interior temperature sensor signal directly, calculates the interior temperature and sends it via interior CAN to the AAC control and operating unit.

• Interior temperature in roof area, in vehicles except CODE 414 (Power glass tilting/sliding roof): 

  The interior temperature in the area of the roof is measured by interior temperature sensor. The overhead control panel electronics read in the signal of the interior temperature sensor directly and send it directly to the automatic air conditioning control and operating unit.

• Interior temperature in center console area: 

  The interior temperature in the area of the center console is measured by interior temperature sensor. The automatic air conditioning control and operating unit reads in the signals of the interior temperature sensor directly.

The stationary heater function encompasses the following subfunctions:

• Function sequence for teaching in radio remote control transmitter 
• Function sequence for setting a departure time 
• Function sequence for triggering ventilation/heating mode 
• Function sequence for ventilation/heating mode 
• Function sequence for terminating ventilation/heating mode 

Function sequence for teaching in radio remote control transmitter 

The individual components of the stationary heater have already been tuned to one another at the factory. Teaching in is only necessary when replacing the radio remote control receiver or radio remote control transmitter. To teach in the radio remote control transmitter, press the stationary heater button in the upper control panel control unit for approx. t = 20 s. The upper control panel control unit reads in the status of the stationary heater button directly and sends this via instrument panel LIN, front SAM control unit and interior CAN to the stationary heater control unit. This sends the request to open the teach-in window to the radio remote control receiver. This then opens the teach-in period window for a maximum t = 5 s. When the teach-in period window is open, the stationary heater control unit sends a corresponding signal via interior CAN, front SAM control unit and instrument panel LIN to the upper control panel control unit. The upper control panel control unit actuates the indicator lamp in the stationary heater button directly.

If the red indicator lamp in the stationary heater button flashes, press and hold the "OFF" button on the radio remote control transmitter until the display shows the message "OFF" (at least t = 1 s). The radio remote control transmitter then issues a radio signal. The radio remote control receiver receives this radio signal directly (except CODE 386 (Comfort telephony) and as of 01.06.2015 with CODE 386 (Comfort telephony)) over the multifunction antenna or over the antenna splitter (up to 31.05.2015 with CODE 386 (Comfort telephony)) and the multifunction antenna. The radio remote control receiver then saves the radio remote control transmitter as assigned to it, and closes the teach-in window. To teach in another radio remote control transmitter, the teach-in window must be opened again. The radio remote control receiver can store up to three radio remote control transmitters. If a fourth radio remote control transmitter is to be taught in, the first radio remote control transmitter that was taught in is deleted.

Using the diagnostic tester the teach-in window can be opened, the time period of which can be configured and the number of radio remote control transmitters that have undergone teach-in can then be read out.

Function sequence for setting a departure time 

The departure time can be configured, selected and activated via the menu structure in the instrument cluster or the radio remote control transmitter. Up to three departure times can be configured. If a departure time was activated, the yellow indicator lamp in the stationary heater button lights up. To do so, the stationary heater control unit sends the "Preselection time activated" status via interior CAN, front SAM control unit and instrument panel LIN to the upper control panel control unit. The upper control panel control unit then actuates the indicator lamp in the stationary heater button directly.

• Activating the departure time via the menu structure in the instrument cluster: 

  To set the departure time through the menu structure in the instrument cluster, call up the "Heater" submenu in the "Settings" menu. The departure time can now be configured, selected or activated. The respective action is shown in the multifunction display of the instrument cluster. The instrument cluster then sends the activated departure time via interior CAN to the stationary heater control unit, which saves this and sends it back to the instrument cluster. The instrument cluster also saves the activated departure time.

• Activating the departure time with the radio remote control transmitter: 

  To select a departure time, press one of the arrow keys. The first of three possible departure times is displayed. Press one of the arrow keys again. The second departure time is shown. Press one of the arrow keys once more. The third departure time is shown. The displayed departure time can be programmed in configuration mode. To do so, press the "ON" and "OFF" buttons at the same time (within t < 0.7 s). The clock symbol in the display of the radio remote control transmitter flashes. The departure time can now be set using the arrow keys. To accept the newly configured departure time, press the "ON" and "OFF" buttons again at the same time. To activate the departure time, press the "ON" button after calling up the required departure time.

  The radio remote control transmitter sends a corresponding radio signal (activated departure time) directly (except CODE 386 (Comfort telephony) and as of 01.06.2015 with CODE 386 (Comfort telephony)) over the multifunction antenna or over the antenna splitter (up to 31.05.2015 with CODE 386 (Comfort telephony)) and the multifunction antenna to the radio remote control receiver. The radio remote control receiver sends the signal directly to the stationary heater control unit, which saves the signal and sends it back over the interior CAN to the instrument cluster.

  To deactivate the departure time, press the "OFF" button after calling up the required departure time. The display of the radio remote control transmitter shows the stationary heater operating condition.

The display options are listed in the separate description "Stationary heater radio remote control receiver, component description". The display period can be configured using the diagnostic tester in 2-second steps (t = 4 to 30 s).

Function sequence for triggering ventilation/heating mode 

Ventilation/heating mode can be activated immediately or preprogrammed:

• Activation via the stationary heater button (immediate mode) 
• Activation via the radio remote control transmitter (immediate mode) 
• Activation when the starting time has been reached (departure time activated) 

Activation via the stationary heater button (immediate mode) 

The ventilation/heating mode is requested by pressing the stationary heater button. The upper control panel control unit reads in the status of the stationary heater button directly and sends this via instrument panel LIN, front SAM control unit and interior CAN to the stationary heater control unit. The stationary heater control unit then sends the "Ventilate" or "Heat" request via interior CAN to the AAC control and operating unit. Ventilation/heating mode is activated in accordance with the feedback.

The rest of the procedure is described in the ventilation/heating mode subfunction.

Activation via the radio remote control transmitter (immediate mode) 

The ventilation/heating mode is requested by pressing the "ON" button on the radio remote control transmitter. The radio remote control transmitter issues a corresponding radio signal (switch-on signal). The stationary heater control unit receives this over the radio remote control receiver. The radio remote control receiver receives the radio signals from the radio remote control transmitter directly (except CODE 386 (Comfort telephony) and as of 01.06.2015 with CODE 386 (Comfort telephony)) over the multifunction antenna or over the antenna splitter (up to 31.05.2015 with CODE 386 (Comfort telephony)) and the multifunction antenna. The stationary heater control unit then sends the "Ventilate" or "Heat" query via interior CAN to the AAC control and operating unit. Ventilation/heating mode is activated in accordance with the feedback.

The rest of the procedure is described in the ventilation/heating mode subfunction.

The range of the radio remote control transmitter is maximum s = 300 m (outdoors). The following influences can reduce the maximum range:

• Radio interference
• solid obstacles (e.g. enclosed premises)
• Unfavorable position to the vehicle

If the radio signal does not reach the radio remote control receiver, this is displayed on the radio remote control transmitter.

Activation when the starting time has been reached (departure time activated) 

Approx. 60 min prior to the activated departure time, the instrument cluster requests the ventilation/heating duration required to reach the configured specified temperature on the AAC control and operating unit via interior CAN. The AAC control and operating unit then calculates the required ventilation/heating duration based on a comparison of the specified interior temperature with the actual interior temperature. The AAC control and operating unit sends the required ventilation/heating duration via interior CAN to the instrument cluster, which then uses the ventilation/heating duration and the current time to calculate the switch-on time. Once the switch-on time is reached, the instrument cluster sends the request to switch on the stationary heater via interior CAN to the stationary heater control unit. The stationary heater control unit then sends the "Ventilate" or "Heat" query via interior CAN to the AAC control and operating unit. Ventilation/heating mode is activated in accordance with the feedback.

The yellow indicator lamp in the stationary heater button goes out.

A switch-on signal sent by the instrument cluster because of an activated departure time is ignored if the ventilation/heating mode was manually triggered in the meantime.

The rest of the procedure is described in the ventilation/heating mode subfunction.

Additional function requirements for ventilation/heating mode 

• Ventilation/heating mode request present
• Remaining quantity of fuel > fuel reserve (minimum fill level)

When circuit 15 is switched off, the stationary heater control unit saves the fuel level. The instrument cluster sends the "Fuel level" signal over the chassis CAN (up to 28.02.2013) or chassis CAN 2 (as of 01.03.2013), front SAM control unit and interior CAN to the stationary heater control unit. The electronic ignition lock control unit sends the status of circuit 15 via interior CAN to the stationary heater control unit.

Function sequence for ventilation/heating mode 

When ventilation/heating mode is activated, the status of all components involved in heating mode is queried first. If faults are detected, the heating mode is not started. The determined fault is verified by a self-test. The result of this self-test updates the status, meaning that heating is possible again if required when the next switch-on attempt occurs (depending on the result). The ventilation mode can always be activated, regardless of the test result.

The following components are tested when starting and in heating mode for any open circuits, short circuits and proper operation:

• Stationary heater temperature sensor
• Stationary heater thermal fuse
• Stationary heater combustion air blower
• Stationary heater glow plug/flame monitor unit
• Stationary heater fuel preheater heating element (with diesel engine)
• Stationary heater fuel shutoff valve (with diesel engine)
• Stationary heater switchover valve
• Stationary heater fuel pump

A defective stationary heater switchover valve does not result in interruption of the heating mode or its start because this component is not relevant for the safe stationary heater operation.

The automatic air conditioning control and operating unit decides whether heating or ventilation is required based on the comparison between the specified and the actual interior temperature. After t = 2 s, the automatic air conditioning control and operating unit transmits the "Ventilate" or "Heat" request via the interior CAN to the stationary heater control unit.

The indicator lamp in the stationary heater button signals the operating mode:

• Ventilation mode, the blue indicator lamp lights up
• Heating mode, the red indicator lamp comes on

To do so, the stationary heater control unit sends the "Stationary heater/stationary ventilation active" status via interior CAN, front SAM control unit and instrument panel LIN to the upper control panel control unit. The upper control panel control unit then actuates the corresponding indicator lamp in the stationary heater button directly.

Ventilation mode 

In ventilation mode, the automatic air conditioning control and operating unit directly actuates the blower regulator. The blower regulator regulates the blower motor speed. With the basic setting, the maximum ventilation time is t = 30 min. This time can be changed using the diagnostic tester in t = 10 minute steps between t = 10 and 60 min. The following shortening factors can also be set:

• Factor 1: Ventilation duration = 3/4 heating duration
• Factor 2: Ventilation duration = 1/2 heating duration
• Factor 3: Ventilation duration = 1/4 heating duration

The ventilation mode can be stopped manually via the radio remote control transmitter or the stationary heater button.

With circuit 15 ON, the blower motor is actuated directly via the blower regulator depending on the setting selected on the AAC control and operating unit. Ventilation mode goes into the background. The indicator lamp in the stationary heater button continues to light up in blue.

Heating mode 

The stationary heater control unit starts the heating mode by actuating the combustion air blower in the heater. The glow plug 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 stationary heater fuel pump begins delivering fuel. The stationary heater fuel pump is actuated directly by the stationary heater control unit. The fuel that evaporates on a metallic mesh 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 their rotational speed and output to wide open throttle within the next t = 60 s.

During the heating mode, the glow plug/flame monitor unit, in its function as flame monitor, reports:

• "hot" = sufficient combustion

  Heating mode continues. Depending on the interior temperature, a switchover from heating mode to ventilation mode or vice versa can take place.

• "cold" = no flame

  Flame-out or insufficient flame formation, the stationary heater fuel pump is switched off and a one-off repeat startup is initiated. If flame formation is still not possible, the stationary heater fuel pump is switched off and the emergency shutoff activated with combustion air blower run-on.

The heating mode is controlled automatically as a function of the coolant temperature. Possible states are:

• Full load operation
• Partial load operation
• Control interval

During heating mode, the coolant is continuously recirculated and gives off its heat into the vehicle interior via the heat exchanger. The automatic air conditioning control and operating unit sends the switch-on request of the coolant circulation pump via interior CAN to the front SAM control unit. This then directly actuates the coolant circulation pump. The coolant is heated in the heater. When a coolant temperature of T = 40 °C is reached in the heater unit, the stationary heater control unit sends the "Switch on blower" request via interior CAN to the AAC control and operating unit. The automatic air conditioning control and operating unit actuates the blower regulator directly. The blower regulator regulates the blower motor speed. The coolant temperature in the heater unit is recorded by the stationary heater temperature sensor. The stationary heater control unit reads in the signals of the stationary heater temperature sensor directly.

From a coolant temperature of T = 60 °C onwards, the stationary heater control unit directly actuates the stationary heater switchover valve. The heated coolant is then used to preheat the engine. The CDI control unit (N3/9) (with diesel engine) or the ME-SFI [ME] control unit (N3/10) (with gasoline engine) sends information on the coolant temperature over the chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013), front SAM control unit and interior CAN to the stationary heater control unit.

When the time of departure is reached, the stationary heater remains switched on for t = 5 minutes and then switches off automatically. With the basic setting, the maximum heating time is t = 30 min. This time can be changed using the diagnostic tester in steps of t = 10 minutes between t = 10 and 60 minutes.

If the engine is started during the heating mode, the expiration of the heating time is ignored and heating continues until the difference between the engine's coolant temperature and the coolant temperature at the heater unit's outlet is a maximum of T = 5 °C.

The heating mode can be stopped manually via the radio remote control transmitter or the stationary heater button.

Function sequence for terminating ventilation/heating mode 

In addition to stopping it manually using the radio remote control transmitter or the stationary heater button, the ventilation/heating mode can also be stopped automatically. The stationary heater control unit continuously checks the function of all components involved for this purpose. Ventilation/heating mode is stopped automatically under the following conditions:

• Overheating of the heater
• Undervoltage
• Crash

Overheating of the heater 

When a temperature of T = 125 °C is exceeded in the heater, the stationary heater is switched off with subsequent overheating locking. The temperature in the heater unit is recorded by the temperature sensor. The signals from the temperature sensor are read in directly by the stationary heater control unit. The stationary heater control unit switches the stationary heater off.

After being switched off startup takes place:

1. Press stationary heater button for t = 5 to 15 s
2. Remove fuse 202 (F58f202) within t = 30 s
3. Reinsert fuse 202

For additional protection, the thermal fuse is activated at a temperature of T = 145 °C. The stationary heater is no longer supplied with fuel.

Undervoltage 

If the on-board electrical system voltage drops below U = 11.8 V, the stationary heater control unit switches off the stationary heater. The front SAM control unit sends the request to switch off the stationary heater via interior CAN to the stationary heater control unit.

Detailed information about the consumer shutoff can be found in the "Energy Management Function" function description.

Crash 

In the event of an accident, the supplemental restraint system control unit sends the crash signal over the chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013), front SAM control unit and the interior CAN to the stationary heater control unit. The stationary heater control unit then switches the heater off permanently. Shutoff can only be reset using the diagnostic tester.