Part 2
GF83.70-P-0006CE Stationary Heater (STH), Function
MODEL 204
- with CODE (228) Stationary heater
Function sequence for checking the component status
When activating the stationary heater, first the status of all components participating in the heating mode is queried. If faults are found, no switch-on attempt is made.The determined faults are verified with a self-test.
The result of the self-test updates the status so that - depending on the result - heating is made possible again upon the next switch-on attempt, where applicable. The stationary ventilation function, however, can always be activated, irrespective of the test result.
The following components are tested for open circuit, short circuit and proper operation during start-up and during heating mode:
- Switchover valve
- Temperature sensor
- Temperature fuse
- Combustion air blower
- Glow plug/flame monitor unit
- Stationary heater fuel pump
A defect at the switchover valve does not result in interruption of the heating mode or its start-up because this component is not relevant for the safe operation of the stationary heater.
Furthermore, the tank content is also queried during start-up of the stationary heater.
To this end, and when circuit 15 is switched off, the instrument cluster sends information on the fuel tank fill level via chassis CAN front SAM control unit and interior CAN to the stationary heater control unit, which then stores it. 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 query is ended positively, the stationary heater control unit sends the query "Ventilate" or "Heat" via interior CAN to the control and operating unit.
Whether heating or ventilation is performed is determined by the control and operating unit after a comparison of the specified interior temperature to the actual interior temperature.
Depending on this comparison and the current setting at the control and operating unit, this decides between "Ventilate" or "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 indicator lamp in the stationary heater button lighting up.
- Indicator lamp red: stationary heating
- Indicator lamp blue: stationary ventilation
The stationary heater control unit sends the status of the stationary heater via interior CAN, front SAM control unit and instrument panel LIN to the upper control panel control unit, which actuates the indicator lamp accordingly.
Additional function requirements for ventilation or heating mode
^ Circuit 15 OFF (valid for ventilation mode)
The electronic ignition lock control unit sends the status of circuit 15 via interior CAN to the stationary heater control unit.
Function sequence for ventilation or heating mode
During ventilating mode, the control and operating unit actuates the blower regulator directly.
The blower regulator controls the rotational speed of the blower motor.
With circuit 15 ON, the blower motor is actuated according to the setting selected at the control and operating unit.
The stationary ventilation function moves to the background.
The indicator lamp in the stationary heater button continues to light up blue.
If the comparison of specified/actual values for the outside and interior temperature result in the "Heat" request, the stationary heater control unit starts heating mode by switching on the stationary heater unit.
The detailed description of the heating mode in the stationary heater control unit is available in the separate "Stationary heater control unit component description" document.
Heater operation is controlled automatically as a function of the coolant temperature. Possible states are:
- Full load operation
- Partial load operation
- Control interval
Following the decision for "Heat", the control and operating unit sends the "Coolant circulation pump ON" request via interior CAN to the front SAM control unit. The front SAM control unit actuates the coolant circulation pump directly.
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 switch hover 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.
The activation of immediate mode via the radio remote control transmitter is described in the "Operation with the radio remote control transmitter" subfunction.
Pressing the stationary heater button activates the stationary heater.
The upper control panel control unit evaluates the air heater button 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" query via 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.
Additional function requirements for programming the departure time
^ Circuit 15R ON (programming via instrument cluster)
The status of circuit 15R is sent by the electronic ignition lock control unit via interior CAN to the instrument cluster.
Function sequence for programming the departure time
The departure time can be programmed using the "Settings" menu in the "Heating" operating level in the instrument cluster or via the radio remote control transmitter.
The programming of the departure time via the radio remote control transmitter is described in the "Operation with the radio remote control transmitter" subfunction.
If the departure time is programmed via the operating level in the instrument cluster, this is shown in the multifunction display of the instrument cluster.
The instrument cluster sends the selected departure time via interior CAN to the stationary heater control unit, which stores the departure time and reports this back to the instrument cluster. The instrument cluster also stores the selected departure time.
If a departure time has been activated, the yellow indicator lamp in the stationary heater button lights up.
The stationary heater control unit sends the corresponding request for this 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 yellow indicator lamp in the stationary heater button.
A maximum of three departure times can be programmed, but only one can be activated.
Additional function requirements for triggering ventilation/ heating mode for the departure time
^ Circuit 15C OFF, exception: Between activation of the departure time and the switching on of the stationary heater, circuit 15C was constantly on.
^ Activated departure time
The status of circuit 15C is sent by the electronic ignition lock control unit via interior CAN.
Function sequence for triggering ventilation/heating mode for the departure time
The instrument cluster queries the required ventilation/heating duration for the set specified temperature via interior CAN from the control and operating unit approx. t = 60 min. before the desired departure time.
The control and operating unit then calculates the required ventilating/heating duration based on the comparison of the specified interior temperature to the actual interior temperature.
The control and operating unit evaluates the following temperature values for this:
- Ambient temperature
- Interior temperature (in roof area)
- Interior temperature in instrument panel area
Using the determined temperature values, the control and operating unit calculates the difference between the specified value and the actual value and determines the required ventilating/ heating duration.
The control and operating unit sends the required ventilating/ heating duration via interior CAN to the instrument cluster, which uses the ventilating/heating duration and the current time to calculate the switch-on time.
If 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 "Heat" or "Ventilate" query via interior CAN to the control and operating unit.The stationary heater is activated in accordance with the feedback. The yellow indicator lamp goes out.
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.
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 heating 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 stationary heater fuel pump.
If the engine is started during heating mode, the stationary heater control unit ignores the expiration of the heating time and continues heating until the difference between the coolant temperature of the engine (large circuit) and the temperature of the coolant at the heater unit's coolant outlet is maximum T = 5 °C.
The CDI control unit or the ME-SFI [ME] control unit sends information on the coolant temperature via chassis CAN, front SAM control unit and interior CAN to the stationary heater control unit.
Function sequence, terminate ventilation mode
The ventilation time 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 minute steps between t = 10 min and 60 min using the diagnostic tester.
In addition to this, a reduction factor can be set.
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 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 start-up takes place:
- via the diagnostic tester or
- by brief interruption of the power supply (fuse removal). For safety reasons proceed as follows here:
1. Press stationary heater button for at least t= 5 to maximum 15 s
2. Remove fuse within t=30s
3. 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 front SAM control unit.If the voltage drops below U = 11.8 V, the front SAM control unit switches off the power supply to the stationary heater.
The detailed consumer shutoff upon undervoltage function can be found in the separate "Engine OFF energy management function" description
Function sequence, safety shutoff due to crash
In the event of an accident, the supplemental restraint system control unit sends the request to switch off the stationary heater via chassis CAN, front SAM control unit and interior CAN to the stationary heater control unit. The heater is then permanently switched off. Resetting the shutoff is only possible using the diagnostic tester.
