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Stationary Heater (STH), Function - GF83.70-P-0006RF

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Model 205, 253 

with code 228 (Auxiliary heater) 

G14188759Courtesy of MERCEDES-BENZ USA

Shown on model 205, 253 

Stationary heater (STH), general 

The stationary heater ensures that the vehicle interior is temperature-controlled and that the windows are clear of ice and fogging before setting off during the colder times of the year. 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:

The radio remote control receiver (with code B24 (Remote control for stationary heater)) or a smartphone, tablet or a PC (with code 11U (Remote Online) or with code 08U (Vehicle setup) or with code 05U (Remote Online)) saves the current operating status of the stationary heater.

The stationary heater control unit continuously sends information about the operating condition of the stationary heater via climate control LIN 2 to the A/C control unit.

With code B24 (Remote control for stationary heater), the climate control control unit sends this via the climate control LIN to the radio remote control receiver. The stored information can be retrieved via the radio remote control transmitter.

The climate control control system sends information about the operating status over the interior CAN, electronic ignition lock control unit and the diagnostics CAN with code 05U (Remote Online) to the telematics services communication module (with code 350 (eCall Europe emergency call system) or with code B54 (Live Traffic Information)) or with code 08U (Vehicle setup) or with code 11U (Remote Online) to the HERMES control unit (with code 362 (HERMES LTE)). The information that is stored there can be retrieved using a smartphone, a tablet or a PC.

The information is provided by request only.

The heater unit is the main component in the STH. It contains all components necessary to generate heat. The heater unit is integrated directly into the engine's heating and cooling circuit and is supplied with fuel by the stationary heater fuel pump. As master of the stationary heater function, the A/C control unit evaluates all variables and communicates with the stationary heater control unit over the climate control LIN 2. To activate the heating mode, the A/C control unit sends the heating request to the stationary heater control unit over the climate control LIN 2.

Operation of the stationary heater requires determination of the following temperatures:

The outside temperature is recorded by the outside temperature sensor. The front SAM control unit reads in the signal of the outside temperature sensor directly, calculates the outside temperature and transmits it to the A/C control unit over the interior CAN.

The interior temperature is recorded by the interior temperature sensor with the integrated fan that is incorporated into the overhead control panel control unit. The front SAM control unit reads in the value of the interior temperature via roof LIN and transmits this via interior CAN to the climate-control control unit.

The stationary heater function comprises the following partial functions:

Function sequence for teaching in the radio remote control transmitter (with CODE B24 (Remote control for stationary heater)) 

The individual components of the stationary heater have already been tuned to each other in 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 climate control operating unit for approx. t = 20 s. The radio remote control receiver opens the teach-in window for maximum t = 5 s. 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 lights up and the "OFF" message is shown.

The radio remote control transmitter then outputs a radio signal. The radio remote control receiver receives the radio signals

The radio remote control receiver stores the radio remote control transmitter as its assigned transmitter and closes the teach-in window. To teach in another radio remote control transmitter, the teach-in period 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 taught in, the first radio remote control transmitter that was taught in is overwritten.

IMPORTANT Using the diagnostic tester, the teach-in window can be opened, its time period can be configured, and the number of teach-in processes can be read out.

The climate control operating unit evaluates the status of the stationary heater button and transmits this to the climate control control unit via the climate control LIN. The A/C control unit sends the request to open the teach-in period window to the radio remote control receiver via the climate control LIN. When the teach-in period window is open, the climate control control unit actuates the indicator lamp in the stationary heater button in the climate control operating unit via the climate control LIN.

Function sequence for setting a departure time 

The departure time can be adjusted, selected and activated through the air conditioning menu in the head unit, over the radio remote control transmitter (with code B24 (Remote control for stationary heater)) or web-based using a browser with a smartphone, tablet or a PC (with code B24 (Remote control for stationary heater) and with code 11U (Remote Online) or with code 08U (Vehicle setup) or with code 05U (Remote Online)). 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 climate control control unit transmits the status "Preselection time activated" to the climate control operating unit via the climate control LIN. The climate control operating unit then actuates the yellow indicator lamp directly in the stationary heater button.

After calling up the climate control menu and selecting the stationary heater, the menu for selecting, modifying and activating the departure time opens. Navigation in the operating menu takes place using the Audio/COMAND® control panel. The relevant requests for selecting the departure time are sent to the head unit by the Audio/COMAND® control panel via telematics CAN. The control requests are shown graphically in the Audio/COMAND® display. The head unit generates the corresponding image data and sends a switch-on request to the Audio/COMAND® display via telematics CAN. The image data is transmitted via the HSVL line to the Audio/COMAND® display. Parallel to this, the head unit transmits information about the settings that have been made via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the climate control control unit. The A/C control unit then sends the activated departure time via interior CAN, electronic ignition lock control unit and user interface CAN to the instrument cluster, which stores this.

To activate the departure time, press the "ON" button after calling up the required departure time.

The radio remote control transmitter issues a corresponding radio signal (activated departure time). The radio remote control receiver receives the radio signals

The radio remote control receiver transmits this via the climate control LIN to the A/C control unit.

The A/C control unit then sends the activated departure time via interior CAN, electronic ignition lock control unit and user interface CAN to the instrument cluster, which stores this.

To deactivate the departure time, press the "OFF" button after calling up the required departure time. The stationary heater operating condition is shown on the display.

IMPORTANT Possible displays are covered in a separate document. The display duration can be adjusted using the diagnostic tester in the stationary heater control unit in 2-second increments (between t = 4 and 30 s).

For web-based programming of the departure time, the telematics services communication module (with code 350 (eCall Europe emergency call system) or with code B54 (Live Traffic Information)) receives the corresponding requests over the communication module/stationary heater antenna and the communication module/stationary heater antenna splitter or the HERMES control unit (with code 360 (HERMES UMTS) or with code 362 (HERMES LTE)) over the emergency call system antenna and with code 362 (HERMES LTE) also over the left telephone antenna or the right telephone antenna, and the telephone antenna splitter, and sends them over the diagnostics CAN, electronic ignition lock control unit and the interior CAN to the climate control control unit.

The A/C control unit then sends the activated departure time via interior CAN, electronic ignition lock control unit and user interface CAN to the instrument cluster, which stores this.

Function sequence for triggering ventilation/heating mode 

The ventilation/heating mode can be triggered immediately or preprogrammed:

Triggering immediate mode 

Immediate mode can be triggered using the following controls:

Triggering via the stationary heater button 

The ventilation/heating mode is requested by pressing the stationary heater button. The climate control operating unit reads in the status of the stationary heater button directly and transmits this to the climate control control unit via the climate control LIN. The A/C control unit decides whether heating or ventilation is required after comparing the specified and the actual interior temperature.

IMPORTANT The subsequent procedure is described in the function sequence for "Ventilation/heating mode".

Triggering via the radio remote control transmitter (with CODE B24 (Remote control for stationary heater)) 

The ventilation/heating mode is requested by pressing the "ON" button (t = 1.5 s) on the radio remote control transmitter. The radio remote control transmitter issues a corresponding radio signal (switch-on signal). The radio remote control receiver receives the radio signals

The radio remote control receiver transmits this via the climate control LIN to the A/C control unit. The A/C control unit decides whether heating or ventilation is required after comparing the specified and the actual interior temperature.

IMPORTANT The subsequent procedure is described in the function sequence for "Ventilation/heating mode".

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

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

Triggering via smartphone, tablet or PC (with code 11U (Remote Online) or with code 08U (Vehicle setup) or with code 05U (Remote Online)) 

The ventilation/heating mode can be requested directly using a Smartphone, a tablet or a PC. The corresponding requests are received by the telematics services communication module (with code 350 (eCall Europe emergency call system) or with code B54 (Live Traffic Information)) over the communication module/stationary heater antenna and the communication module/stationary heater antenna splitter or the HERMES control unit (with code 360 (HERMES UMTS) or with code 362 (HERMES LTE)) over the emergency call system antenna and sends them over the diagnostics CAN, electronic ignition lock control unit and the interior CAN to the climate control control unit. The A/C control unit decides whether heating or ventilation is required after comparing the specified and the actual interior temperature.

IMPORTANT The subsequent procedure is described in the function sequence for "Ventilation/heating mode".

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

Approx. 60 min before the activated departure time, the instrument cluster requests the required ventilation/heating duration to achieve the set specified temperature from the climate control unit via the user interface CAN, electronic ignition lock control unit and interior CAN. The climate control control unit then calculates the required ventilation/heating duration based on a comparison of the specified interior temperature with the actual interior temperature.

The A/C control unit sends the required ventilation/heating duration via interior CAN, electronic ignition lock control unit and user interface CAN to the instrument cluster, which calculates the switch-on time from the ventilation/heating duration and the current time. Once the switch-on time is reached, the instrument cluster sends the request to ventilate or heat over the user interface CAN, electronic ignition lock control unit and interior CAN to the climate-control control unit.

IMPORTANT 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.

IMPORTANT The subsequent procedure is described in the function sequence for "Ventilation/heating mode".

Additional function requirements for ventilation/heating mode 

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, heating mode is not started. The fault that has been detected is verified by means of a self-test. The result of this self-test updates the status so that heating can continue if necessary when the next switch-on attempt occurs, depending on the result. 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:

For this purpose, the climate control control unit sends the "Stationary heater/stationary ventilation active" status via the climate control LIN to the climate control operating unit, which actuates the indicator lamp in the stationary heater button accordingly.

Ventilation mode

In ventilation mode, the climate-control control unit actuates the blower regulator via climate control LIN 2. The blower regulator controls the speed of the blower motor. With the basic setting, the maximum ventilation time is t = 50 min. These can be changed using the diagnostic tester in 5-minute increments between t = 10 and 60 min.

IMPORTANT The ventilation mode can be manually ended using the stationary heater button, radio remote control transmitter (with code B24 (Remote control for stationary heater)) or web-based with a smartphone, tablet or a PC (with code 11U (Remote Online) or with code 08U (Vehicle setup) or with code 05U (Remote Online)).

IMPORTANT With circuit 15 On, the blower motor is actuated directly via the blower regulator depending on the setting selected on the climate-control control 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, and a flame is formed. The glow plug then becomes a flame monitor. The combustion air blower and 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:

IMPORTANT A defect at the switchover valve does not result in interruption of the heating mode or inhibit its startup because this component is not relevant for the safe operation of the stationary heater. The climate-control control 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 climate control control unit sends the "Heat" request (0 - 100 %) via climate control LIN 2 to the stationary heater control unit, which implements this request accordingly.

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

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

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 continuously regulated in a range of 50 to 100 %, to keep the coolant temperature at a constant value.

Following the "Heat" decision, the A/C control unit actuates the coolant circulation pump directly. The coolant is heated in the heater. When a coolant temperature of T = 50°C is reached in the heater, the climate control control unit actuates the blower motor via the blower regulator. The coolant temperature in the heater unit is recorded by the stationary heater temperature sensor. The stationary heater control unit reads in the signal of the stationary heater temperature sensor directly.

The A/C control unit transmits the request to actuate the stationary heater switchover valve over the climate control LIN 2 to the stationary heater control unit. The stationary heater control unit actuates the stationary heater switchover valve directly.

IMPORTANT When the time of departure is reached, the stationary heater remains switched on for t = 5 min and then switches off automatically. Unless the engine is started, in which case the STH switches off immediately. With the basic setting, the maximum heating duration is t = 50 min. These can be changed using the diagnostic tester in 5-minute increments between t = 10 and 60 min.

IMPORTANT If the engine is started during heater operation, the expiration of the heating duration is ignored and heating continues until the difference between the coolant temperature in the engine and the coolant temperature at the heater outlet is a maximum of T = 5°C.

IMPORTANT The heating mode can be manually ended using the stationary heater button, the radio remote control transmitter (with code B24 (Remote control for stationary heater)) or web-based through the corresponding application program (with code 11U (Remote Online) or with code 08U (Vehicle setup) or with code 05U (Remote Online)).

Function sequence for terminating ventilation/heating mode 

Ventilation/heating mode can be terminated either manually or automatically before the departure time is reached. 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

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

Startup after being switched off:

  1. Press stationary heater button for t = 5 to 15 s.
  2. Remove electrical fuse 318 (F1/3f318) within t = 30 s.
  3. Reinsert electrical fuse 318.

IMPORTANT For additional protection, the stationary heater thermal fuse is triggered 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 climate control control unit switches off the STH. The front SAM control unit sends the request to switch off the stationary heater via interior CAN to the A/C control unit. When the STH is switched on, the climate control control unit activates the STH emergency shutoff and sends the "Heat" request (0 %) via climate control LIN 2 to the stationary heater control unit. The heater is then permanently switched off.

Accident (crash)

In the event of an accident, the stationary heater is automatically turned off (reduces risk of fire). The supplemental restraint system control unit transmits the crash signal via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the A/C control unit. When the STH is switched on, the climate control control unit activates the STH emergency shutoff and sends the "Heat" request (0 %) via climate control LIN 2 to the stationary heater control unit. The heater is then permanently switched off. Resetting the shutoff is only possible using the diagnostic tester.

Additional function requirements for heat boosting mode 

Function sequence for heat boosting mode 

Pressing the stationary heater button activates the heater booster.

The climate control operating unit reads in the status of the stationary heater button and transmits this to the climate control control unit via the climate control LIN. Regardless of the outside temperature and the position of the blend air flaps, the A/C control unit transmits the "Heat" request via climate control LIN 2 to the stationary heater control unit. The stationary heater control unit then starts heater booster mode. At the same time, the A/C control unit actuates the coolant circulation pump directly. The coolant is then circulated in the large coolant circuit. Heater booster mode is signaled by the red indicator lamp in the stationary heater button lighting up. The climate control control unit transmits the request to switch on the indicator lamp via the climate control LIN to the climate control operating unit. The climate control operating unit actuates the indicator lamp directly.

IMPORTANT The detailed description of the heating mode in the heater is described in the ventilation/heating mode function sequence.

IMPORTANT The CDI control unit or the ME-SFI [ME] control unit transmits the "Drivetrain operational" signal and information on the coolant temperature via the drive train CAN, the powertrain control unit, the chassis FlexRay, the electronic ignition lock control unit and the interior CAN to the climate control control unit.

  Electrical function schematic for stationary heater (STH)   PE83.70-P-2050-97FBA
  Electrical function schematic for triggering heater booster mode   PE83.70-P-2060-97FBA
  Overview of system components for stationary heater (STH)   GF83.70-P-9996RF 
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