Function description - ra83001400400x(0400)
auxiliary heating General, Components of aux. heater/radio remote control, mode of operation of function diagram, electrical function, technical data - Model 140
- General
The auxiliary heater is an independent heating system operating separately from the vehicle's engine. To operate, the auxiliary heater is connected to the coolant circuit, fuel system and electrical system of the vehicle.
The auxiliary heater can be switched on when parked and when driving, whenever greater heating capacity is desired.
The auxiliary heater serves to heat the passenger compartment and defrost the vehicle windows. At the same time, the engine is preheated by means of the coolant so that it will fire reliably even when outside temperatures are low.
Do not operate the auxiliary heater in closed rooms without exhaust gas ventilation, even with preselected heating. Switch off the auxiliary heater at filling stations.
- Components of auxiliary heater
Auxiliary heater timer (N34)
Three cut-in times and the desired days of the week can be preprogrammed using the timer (N34). If no day is set, the cut-in times can only be programmed within 24 hours.
When the auxiliary heater is switched on, the timer (N34) sends a signal of approx. 2 seconds' duration to the auxiliary heater control unit (N33).
The electronic system of the auxiliary heater control unit (N33) recognizes the signal as a cut-in signal and the auxiliary heater control unit (N33) switches to standby.
During operation, data passes from the auxiliary heater control unit (N33) to the timer (N34). By the data received, the timer (N34) detects whether operation is normal or whether there is a malfunction. After one hour, or when the
button is pressed, the flow of data is interrupted and the auxiliary heater is switched off.
If there is a malfunction, the auxiliary heater control unit (N33) switches off the auxiliary heater and reports the fault to the timer (N34). The malfunction is indicated in the display of the timer (N34) by an F (Fault).
Auxiliary heater control unit (N33)
When the auxiliary heater is switched on, the control unit (N33) controls the entire function sequence of the heating unit (A6) of the auxiliary heater.
To do this, it evaluates the signals from the flame control (A6r3), temperature sensor (A6b1) and thermal fuse (A6f1).
The function of the individual components is monitored while the heater is operating and any fault occurring is stored in the fault memory of the control unit (N33). The fault memory can be called up for diagnostic purposes.
Heating unit (A6) of auxiliary heater
The fuel-air mixture is burned in the heating unit (A6) and this warms the coolant in the water jacket. The components listed in the key to the illustration are part of the heater assembly (A6) and have the functions described below.
Temperature sensor (A6b1)
The temperature sensor (A6b1) is a PTC resistor which changes its resistance according to the temperature.
The higher the temperature, the higher its resistance. The operating sequence of the heating unit (A6) of the auxiliary heater (full/half heating capacity or combustion interval) is controlled by the temperature sensor via the auxiliary heater control unit (N33).
Thermal fuse (A6f1)
The thermal fuse (A6f1) protects the auxiliary heater (A6) against excessively high operating temperatures.
The thermal fuse (A6f1) is an overheating protection with a melting temperature of 140°C.
Combustion air blower (A6m2)
The combustion air blower (A6m2) delivers the quantity of air necessary for forming the mixture. It is controlled via the auxiliary heater control unit (N33), which receives the necessary information from the temperature sensor (A6b1).
Combustion air blower preresistor (A6r1)
In partial-load operation, the auxiliary heater control unit (N33) connects the preresistor (A6r1) upstream of the combustion air blower (A6m2) so that the combustion air blower (A6m2) only operates at about half speed.
Glow plug (A6r2) / Flame control (A6r3)
The glow plug (A6r2) and flame control (PTC resistor, A6r3) are incorporated into a single unit.
The glow plug (A6r2) generates the heat necessary for starting up the auxiliary heater (A6) and is switched off by the flame control (A6r3) via the auxiliary heater control unit (N33) after combustion has stabilized. The voltage for the glow plug (A6r2) is timed by the auxiliary heater control unit (N33); the lower the battery voltage, the longer the voltage is applied to the glow plug (A6r2). The voltage is continuous when the battery voltage is less than 10 volts.
The flame control (A6r3) is a PTC resistor which changes its resistance according to the temperature and which monitors combustion. The higher the temperature, the greater its resistance. If combustion ceases, the flame control (A6r3) signals this to the auxiliary heater control unit (N33). The auxiliary heater control unit (N33) switches off the auxiliary heater (malfunction shutdown).
Auxiliary heater fuel metering pump (Y23)
The fuel metering pump (Y23) delivers the fuel quantity required for combustion from the fuel tank to the heater (A6).
The fuel metering pump (Y23) is controlled by the auxiliary heater control unit (N33). A valve installed in the suction line prevents the fuel from flowing back into the tank.
Exhaust muffler
The exhaust muffler insulates the combustion noise and directs the exhaust gases into the open air.
Auxiliary heater switch-over valve (Y16)
The switch-over valve (Y16) directs the coolant through the heating unit (A6) to the heat exchanger when the auxiliary heater is operating. The switch-over valve (Y16) is de-energized when the auxiliary heater is switched off and the coolant flows directly from the engine to the heat exchanger.
Thermostat
The thermostat has three separate functions in connection with the coolant circuit of the auxiliary heater.
Up to a coolant temperature of approx. 55°C, the thermostat blocks the coolant supply from the engine to the heater (A6) and the coolant in the engine is not heated.
At coolant temperatures between 55°C and 65°C, the thermostat starts to open and regulates the flow of coolant from the engine to the heater (A6). In this way, the coolant in the engine is heated as well.
At coolant temperatures above 65°C in the engine, the thermostat is fully open and the coolant supply to the heater (A6) comes from the engine alone.
The engine thus forms part of the coolant circuit.
Heating system delivery unit (A31)
Circulating pump (A31m1)
There is no circulating pump at the heater (A6) itself. The coolant is circulated by actuating the standard circulating pump (A31m1) integrated in the heating system delivery unit (A31).
Duo valves (A31y1 and A31y2)
The duo valves (A31y1 and A31y2) are actuated by the automatic heater control unit (N18) and the automatic climate control unit (N22) of the vehicle heating system respectively, and regulate the flow rate of heated coolant through the heat exchanger.
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.
Electrical fuses in the fuse/relay box (F1)
The auxiliary heater is protected against overload and short circuit by two fuses.
The fuses of terminal 30 (F3-33 and F3-36) are located in the 35-fuse holder (F3) in the fuse/relay box (F1).
Fuse 33 20 amps Fuse 36 10 amps Auxiliary heater functions * Blower motor (M2)
* Circulating pump (A31m1)
* Automatic climate control unit (N22)* Only with auxiliary heater switched on
- Components of auxiliary heater radio remote control
Hand-held transmitter for auxiliary heater radio remote control
The hand-held transmitter can only be used to switch the auxiliary heater on. The maximum range is 1000 m.
The range may be less from within closed rooms.
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.
Receiver (A6/1) for auxiliary heater radio remote control
The hand-held transmitter and the receiver (A6/1) installed in the vehicle are coded. The auxiliary heater can therefore only be switched on using the hand-held transmitter corresponding with the receiver (A6/1).
The radio signal emitted by the hand-held transmitter at a frequency between 433.05 MHz and 434.79 MHz is converted into a voltage signal by the receiver (A6/1).
- Mode of operation with function diagram
Switching on using the auxiliary heater timer (N34) or the hand-held transmitter for radio remote control
The green indicator lamp on the timer (N34) lights up when the auxiliary heater is switched on using the timer (N34) or the hand-held transmitter for radio remote control. At the same time, the auxiliary heater switch-over valve (Y16), the circulating pump (A31m1), glow plug (A6r2) and combustion air blower (A6m2) are started up at partial load.
Approx. 30 seconds after switching on, the auxiliary heater fuel metering pump (Y23) starts to deliver the partial-load fuel volume.
A safety period of approx. 90 seconds now commences, in which the flame control (A6r3) must detect combustion.
If combustion is not established approx. 120 seconds after the auxiliary heater is switched on, the fuel metering pump (Y23) is switched off. The glow plug (A6r2), circulating pump (A31m1) and combustion air blower (A6m2) continue to operate.
In the approx. 30 seconds until the start-up is repeated, the combustion air blower (A6m2) switches from partial load to full load to flush out the combustion chamber. Startup is then repeated automatically.
If the flame control (A6r3) still does not detect perfect combustion during repeated starting within approx. 120 seconds, the auxiliary heater control unit (N33) switches off the auxiliary heater (malfunction shutdown).
An F (Fault) appears in the display of the timer (N34).
The circulating pump (A31m1) and the combustion air blower (A6m2 at full load) run on for approx. 60 seconds. After the cause of the malfunction has been rectified, the auxiliary heater must be switched off and on again for the function test to be performed.
Full-load operation (full heating capacity)
Approx. 10 seconds after the flame control (A6r3) has detected the start of combustion, the auxiliary heater control unit (N33) switches the auxiliary heater fuel metering pump (Y23) to full-load operation, followed by the combustion air blower (A6m2) approx. 5 seconds later.
Switching on the heater blower
At a coolant temperature of approx. 30°C, the auxiliary heater control unit (N33) switches on the blower motor (M2) at a fixed speed.
Partial-load operation (approx. half heating capacity)
When the coolant temperature in the heater (A6) reaches approx. 78°C, the heating capacity is reduced to approximately half. The transition from full load to partial-load operation occurs within a period of approx. 20 seconds, in which first the fuel metering pump (Y23) and then the combustion air blower (A6m2) are switched to partial-load operation.
If the coolant temperature then drops to approx. 70°C in partial-load operation, full heating capacity is switched on again.
Start of combustion interval
If the coolant temperature in the heater reaches approx. 86°C in partial-load operation, the auxiliary heater control unit (N33) switches off the fuel metering pump (Y23). The combustion air blower (A6m2) runs on for max. 80 seconds at partial load (temperature-dependent run-on) and approx. 60 seconds at full load (electronic run-on), and is then switched off by the auxiliary heater control unit (N33). The circulating pump (A31m1) and blower motor (M2) continue to operate.
End of combustion interval
The combustion interval ends when the coolant temperature has dropped to approx. 70°C. The glow plug (A6r2), combustion air blower (A6m2) and approx. 30 seconds later the fuel metering pump (Y23) are started up as when switching on.
The start-up phase after the combustion interval is the same as when starting up with the auxiliary heater timer (N34). This alternate switching on and off is repeated until the auxiliary heater is switched off automatically after max. 1 hour or with the auxiliary heater timer (N34).
Switching off at partial load (approx. half heating capacity)
At the end of operation, the fuel metering pump (Y23) and blower motor (M2) are switched off.
The combustion air blower (A6m2) and circulating pump (A31m1) run on for max. 140 seconds. The combustion air blower (A6m2) runs on for max. 80 seconds at partial load (temperature-dependent run-on) and then for approx. 60 seconds at full load (electronic run-on).
The auxiliary heater switch-over valve (Y16) is de-energized, and therefore switched, when the circulating pump (A31m1) is switched off.
Switching off at full load (full heating capacity)
The run-on after the heater is switched off at full load is different from partial load.
The combustion air blower (A6m2) runs at full load for the entire duration of the run-on (max. 140 seconds).
NOTE: In the event of undervoltage < 9.5 V or overvoltage > 16 V, the auxiliary heater control unit (N33) switches off the auxiliary heater.Switching on - combustion interval
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Combustion interval - switching off during full-load operation
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Combustion interval - switching off during partial-load operation
- Electrical function
Switching on using the auxiliary heater timer (N34) or radio remote control
The auxiliary heater control unit (N33) receives voltage via connections 1 and 2 of connector B.
If the auxiliary heater is switched on using the timer (N34) or the hand-held transmitter for radio remote control, the green indicator lamp (auxiliary heater operating) in the timer (N34) lights up.
A signal is sent to the auxiliary heater control unit (N33) via connection 2 of connector D.
The auxiliary heater control unit (N33) then carries out the following functions simultaneously:
It applies voltage to connection 10 of connector C. The auxiliary heater switch-over valve (Y16) switches and allows coolant to flow through the heating unit (A6).
It applies voltage to connection 10 of connector B and switches connection 4 of connection B to ground. The circulating pump (A31m1) of the vehicle heating system is started up via the circulating pump plug connection (X73/1).
It applies voltage to connection 12 of connector C and, at the same time, connection 3 of connector C is routed to ground intermittently. This starts the glow plug (A6r2). The timing of the intermittent grounding is relative to the voltage.
It applies voltage to connection 11 of connector C and routes connection 5 of connector C to ground. The combustion air blower (A6m2) is switched to partial load (approx. half speed) via the combustion air blower preresistor (A6r1).
It applies voltage to connection 3 of connector A. After 30 seconds, it routes connection 1 of connector C to ground intermittently. The fuel metering pump (Y23) starts to deliver the partial-load fuel volume.
This is followed by a safety period of approx. 90 seconds, in which the flame control (A6r3) must detect combustion.
If combustion starts, this is signalled to the auxiliary heater control unit (N33) by the change in resistance of the flame control (A6r3). The auxiliary heater control unit (N33) disconnects ground at connection 3 of connector C. The glow plug (A6r2) stops operating.
In the next 10 seconds, the changing resistance of the flame control (A6r3) tells the auxiliary heater control unit (N33) whether combustion has stabilized.
If it has, the auxiliary heater control unit (N33) increases the timing frequency of the fuel metering pump (Y23) and thus increases its delivery rate to full load.
Five seconds later, the auxiliary heater control unit (N33) switches the ground from connection 5 of connector C to connection 7 of connector C.
The combustion air blower preresistor (A6r1) is disabled and the combustion air blower (A6m2) is switched from partial to full-load operation (full speed).
Switching on the heater blower
When the coolant temperature in the heater (A6) reaches approx. 30°C, the changing resistance of the temperature sensor (A6b1) signals this to the auxiliary heater control unit (N33).
The auxiliary heater control unit (N33) switches on the blower motor (M2) of the vehicle heating systems at a fixed speed via connection 5 of connector B and via the auxiliary heater/heating systems plug connection (X72/1).
Partial-load operation
When the coolant temperature in the heater (A6) reaches approx. 78°C, the changing resistance of the temperature sensor (A6b1) signals this to the auxiliary heater control unit (N33).
The auxiliary heater control unit (N33) halves the timing frequency of the fuel metering pump (Y23), thus reducing the quantity of fuel delivered to partial load.
Within approx. 20 seconds, the auxiliary heater control unit (N33) switches the ground from connection 7 of connector C to connection 5 of connector C.
The combustion air blower preresistor (A6r1) is activated and the combustion air blower (A6m2) is switched from full to partial-load operation (approx. half speed).
Full-load operation after partial-load operation
If the coolant temperature in the heater (A6) drops below approx. 70°C during partial-load operation, the changing resistance of the temperature sensor (A6b1) signals this to the auxiliary heater control unit (N33).
The auxiliary heater control unit (N33) increases the timing frequency of the fuel metering pump (Y23), thus increasing the delivery quantity to full load.
After 5 seconds, the auxiliary heater control unit (N33) switches the ground from connection 5 of connector C to connection 7 of connector C.
The combustion air blower preresistor (A6r1) is disabled and the combustion air blower (A6m2) is switched from partial to full-load operation (full speed).
Start of combustion interval
When the coolant temperature in the heater (A6) reaches approx. 86°C, the changing resistance of the temperature sensor (A6b1) signals this to the auxiliary heater control unit (N33).
The auxiliary heater control unit (N33) disconnects ground from connection 1 of connector C. The fuel metering pump (Y23) is switched off.
The combustion air blower (A6m2) runs on at partial load for a maximum of 80 seconds (temperature-dependent run-on).
Within this period, the changing resistance of the flame control (A6r3) signals to the auxiliary heater control unit (N33) that the flame has gone out.
The auxiliary heater control unit (N33) switches the ground from connection 5 of connector C to connection 7 of connector C. The combustion air blower preresistor (A6r1) is disabled. The combustion air blower (A6m2) runs on at full speed for approx. 60 seconds and is then switched off by the auxiliary heater control unit (N33).
The circulating pump (A31m1), the blower motor (M2) of the vehicle heating system and the auxiliary heater switch-over valve (Y16) remain switched on.
End of combustion interval
If the coolant temperature in the heater (A6) drops to approx. 70°C, the changing resistance of the temperature sensor (A6b1) signals this to the auxiliary heater control unit (N33).
The auxiliary heater control unit (N33) now performs the following functions:
It applies voltage to connection 12 of connector C and, at the same time, connection 3 of connector C is routed to ground intermittently. This starts the glow plug (A6r2). The timing of the intermittent grounding is relative to the voltage.
It applies voltage to connection 11 of connector C and routes connection 5 of connector C to ground. The combustion air blower (A6m2) is switched to partial load (approx. half speed) via the combustion air blower preresistor (A6r1).
It applies voltage to connection 3 of connector A. After 30 seconds, it routes connection 1 of connector C to ground intermittently. The fuel metering pump (Y23) starts to deliver the partial-load fuel volume.
This is followed by a safety period of approx. 90 seconds, in which the flame control (A6r3) must detect combustion.
If combustion starts, this is signalled to the auxiliary heater control unit (N33) by the change in resistance of the flame control (A6r3). The auxiliary heater control unit (N33) disconnects ground at connection 3 of connector C. The glow plug (A6r2) stops operating.
In the next 10 seconds, the changing resistance of the flame control (A6r3) tells the auxiliary heater control unit (N33) whether combustion has stabilized.
If it has, the auxiliary heater control unit (N33) increases the timing frequency of the fuel metering pump (Y23) and thus increases its delivery rate to full load.
Five seconds later, the auxiliary heater control unit (N33) switches the ground from connection 5 of connector C to connection 7 of connector C.
The combustion air blower preresistor (A6r1) is disabled and the combustion air blower (A6m2) is switched from partial to full-load operation (full speed).
Switching off with the timer in controlled operation (combustion interval) with run-on completed
When the auxiliary heater is switched off, the auxiliary heater control unit (N33) performs the following functions:
It switches off the voltage at connection 5 of connector B. The blower motor (M2) of the vehicle heating system is switched off.
It switches off the voltage at connection 10 of connector C. The auxiliary heater switchover valve (Y16) switches and blocks the flow of coolant through the heating unit (A6).
Switching off with the timer or after the heating period has elapsed from partial-load operation
When the auxiliary heater is switched off, the auxiliary heater control unit (N33) performs the following functions:
It switches off the intermittent ground at connection 1 of connector C. The auxiliary heater fuel metering pump (Y23) is switched off.
It switches off the voltage at connection 5 of connector B. The blower motor (M2) of the vehicle heating system is switched off.
The combustion air blower (A6m2) runs on for max. 80 seconds at approx. half speed in partial-load operation (temperature-dependent run-on).
Within 80 seconds, the changing resistance of the flame control (A6r3) signals to the auxiliary heater control unit (N33) that the flame has gone out.
The auxiliary heater control unit (N33) switches the ground from connection 5 of connector C to connection 7 of connector C. The combustion air blower (A6r1) is disabled and the combustion air blower (A6m2) runs on for approx. 60 seconds at full speed in full-load operation (electronic run-on).
The auxiliary heater control unit (N33) then switches off all switching sequences.
Switching off with the timer or after heating period has elapsed from full-load operation
When the auxiliary heater is switched off, the auxiliary heater control unit (N33) performs the following functions:
It switches off the intermittent ground at connection 1 of connector C. The auxiliary heater fuel metering pump (Y23) is switched off.
It switches off the voltage at connection 5 of connector B. The blower motor (M2) of the vehicle heating system is switched off. Within 80 seconds, the changing resistance of the flame control (A6r3) signals to the auxiliary heater control unit (N33) that the flame has gone out.
The combustion air blower (A6m2) runs on for max. 140 seconds at full speed in full-load operation (temperature-dependent, electronic run-on).
The auxiliary heater control unit (N33) then switches off all switching sequences.
Repeated starting if combustion is not established
If combustion is not established approx. 120 seconds after the auxiliary heater is switched on, the auxiliary heater control unit (N33) switches off the intermittent ground at connection 1 of connector C. The fuel metering pump (Y23) is switched off.
The glow plug (A6r2), circulating pump (A31m1) and combustion air blower (A6m2) continue to operate.
In the approx. 30 seconds until start-up is repeated, the auxiliary heater control unit (N33) switches the ground from connection 5 of connector C to connection 7 of connector C.
The combustion air blower preresistor (A6r1) is disabled and the combustion air blower (A6m2) is switched from partial to full-load operation to flush the combustion chamber.
After 30 seconds, it routes connection 1 of connector C to ground intermittently. The fuel metering pump (Y23) starts to deliver the partial-load fuel quantity and the combustion air blower runs at partial load.
This is followed by the safety period of approx. 90 seconds, in which the flame control (A6r3) must detect combustion.
If combustion starts, this is signalled to the auxiliary heater control unit (N33) by the change in resistance of the flame control (A6r3). The auxiliary heater control unit (N33) disconnects ground at connection 3 of connector C. The glow plug (A6r2) stops operating.
In the next 10 seconds, the changing resistance of the flame control (A6r3) tells the auxiliary heater control unit (N33) whether combustion has stabilized.
If it has, the auxiliary heater control unit (N33) increases the timing frequency of the fuel metering pump (Y23) and thus increases its delivery rate to full load.
Automatic cut-out in event of faults
If the auxiliary heater control unit (N33) detects a fault while the auxiliary heater is operating, the auxiliary heater control unit (N33) performs the following functions:
It switches off the intermittent ground at connection 1 of connector C. The fuel metering pump (Y23) is switched off.
It switches off the voltage at connection 5 of connector B. The blower motor (M2) of the vehicle heating system is switched off.
It sends a fault code to the auxiliary heater timer (N34).
If the auxiliary heater is operating at partial load, the combustion air blower (A6m2) runs on for max. 80 seconds at approx. half speed (temperature-dependent run-on).
If the auxiliary heater is operating at full load, the combustion air blower (A6m2) runs on for max. 80 seconds at full speed (temperature-dependent run-on).
Within this period, the changing resistance of the flame control (A6r3) signals to the auxiliary heater control unit (N33) that the flame has gone out.
The auxiliary heater control unit (N33) switches the ground from connection 5 of connector C to connection 7 of connector C. The combustion air blower preresistor (A6r1) is disabled and the combustion air blower (A6m2) runs on for approx. 60 seconds at full speed in full-load operation (electronic run-on).
The auxiliary heater control unit (N33) then switches off all switching sequences and remains blocked (fault shutdown).
The green indicator lamp (auxiliary heater operating) goes out.
After the cause of the fault has been rectified, the fault shutdown can be unlocked by switching the auxiliary heater off and on again using the instant heat button.
NOTE: In the event of undervoltage < 9.5 V or overvoltage > 16 V, the auxiliary heater control unit (N33) switches off the auxiliary heater. - Technical data
| Approx. heating capacity at full load | 4.6 kW |
| Approx. heating capacity at partial load | 2.3 KW |
| Approx. fuel consumption at full load | 0.7 l/h |
| Approx. fuel consumption at partial load | 0.3 l/h |
| Nominal voltage rating | 12 V |
| Operating voltage range | 10-14 V |
| Approx. power input at start-up | 8.3 A |
| Approx. power input at full load | 3.7 A |
| Approx. power input at partial load | 2.8 A |
| Approx. closed-circuit current | 1mA |
| Approx. closed-circuit current with radio remote control | 6mA |
| CO2 in exhaust gas at full load | 9.5-12 vol. % |
| CO2 in exhaust gas at partial load | 7.0-10 vol. % |
| Automatic running time | 1 hour |
| Preselection time with day not set up to | 24 hours |
| Preselection time with day set up to | 1 week |