Ending heater mode, function

S83.70-2525-06

1 Jacket

2 Coolant inlet

3 Coolant outlet

4 Heater core

5 Burner housing

A90 Heater booster

A90.1 Main wiring harness connector to heater booster

A75 Heater booster control module

A75.3 Heater booster connector in electric compartment

B94 Coolant temperature switch

B95 Overheating fuse

B96 Flame monitor

M44 Combustion air blower

M54 Heater booster fuel metering pump

R18 Glow plug

Normal heater operation can be terminated manually on the air conditioning pushbutton control module (A20) with the heater booster switch (A20s6) or by shutting off the engine when the heater operation has not been interrupted by a malfunction.

Heater start-up can be interrupted by the following malfunctions:

 Defective flame monitor

 Lack of flame formation

The following can lead to premature interruption of the heating period during heater operation:

 Overheating,

 Voltage too low or too high

 Flame interruption

 Defective flame monitor or temperature switch

-----------------------------------------------------------------------------------------

Terminating heater operation manually or automatically

1 The combustion is stable. The fuel metering pump (M54) and the combustion air blower (M44) operate at their lowest capacity.

2 The heating mode is terminated manually or automatically.

3 The fuel metering pump (M54) switches off interrupting combustion.

4 The shut-off delay for cooling the heater and for purging the combustion chamber starts for approx. 120 s. The combustion air blower (M44) operates at partial load for approx. 30 s and at full load for approx. 90 s.

5 The shut-off delay is completed. The combustion air blower and the heater auxiliary pump (M10/M45) switch off. Heater operation is terminated.

-----------------------------------------------------------------------------------------

Flame formation missing

1 Following completion of the safety time the flame monitor (B96) is checked.

2 The flame monitor (B96) signals "cold".

3 The fuel metering pump (M54) switches off.

4 The shut-off delay for purging the combustion chamber starts for approx. 60 s. The combustion air blower (M44) operates at partial load during the shut-off delay.

5 The shut-off delay is completed. The start-up operation is repeated. The glow plug (R18) switches on and the new start-up procedure starts with a preglowing time of 32 s, safety time of 85 s and flame monitor (B96) check.

6 The flame monitor (B96) again signals "cold". The heater booster control module (A75) starts a malfunction shut-off.

7 The fuel metering pump (M54) switches off.

-----------------------------------------------------------------------------------------

8 The shut-off delay for cooling the heater and for purging the combustion chamber starts for approx. 130 s. The combustion air blower (M44) operates at partial load for approx. 35 s and at full load for approx. 95 s.

9 The shut-off delay is completed. The combustion air blower and the hot water auxiliary pump (M10/M45) switch off.

 After eliminating the cause of the malfunction, switch the heater off and back on to reset.

-----------------------------------------------------------------------------------------

Heater overheats

1 The heater is operating at partial load or full load.

2 The coolant temperature increases to above 105 °C and thereby reaches an impermissibly high temperature value.

3 The heater booster control module (A75) recognizes overheating, interrupts the fuel metering pump (M54) circuit to protect the heater and initiates a malfunction shut-off with following malfunction lockout.

4 The shut-off delay for cooling the heater and for purging the combustion chamber starts for approx. 120 s. The combustion air blower (M44) previously operating at full load operates for approx. 30 s at partial load and for approx. 90 s at full load.

5 The shut-off delay is completed. The combustion air blower (M44) switches off.

6 The malfunction shut-off is completed. Restarting the defective heater is no longer possible.

 The malfunction lock-out can be reset after eliminating the malfunction by interrupting the power supply.

-----------------------------------------------------------------------------------------

Voltage too low or too high during heater operation

1 The heater is operating at partial or full load.

2 The heater booster control module (A75) recognizes a malfunction in the power supply.

2.1 The voltage is < 9.7 - 10.3 V for more than 20 s.

 The control module starts a malfunction shut-off to protect the battery from discharging.

2.2 The voltage increases to 15.5 V for more than 6 s.

 The control module starts a malfunction shut-off to protect the electric and electronic heater components.

3 The fuel metering pump (M54) switches off interrupting the combustion.

4 The shut-off delay for cooling the heater and for purging the combustion chamber starts for approx. 130 s. The combustion air blower (M44) operates at partial load for approx. 35 s and at full load for approx. 95 s.

5 The shut-off delay is completed. The combustion air blower (M44) switches off.

-----------------------------------------------------------------------------------------

Flame interruption or defective flame monitor

1 The heater is operating at partial load or full load.

2 The flame monitor (B96) signals "cold". This message can be caused by insufficient fuel or combustion air feed or by a defective flame monitor.

3 The heater booster control module (A75) starts again for approx. 85 s for new flame formation and continuation of the combustion.

4 The combustion air blower (M44) and the fuel metering pump (M54, diesel version) switch from previously full load to partial load. The fuel metering pump (M54, gasoline version) remains at or is switched to full load.

5 The glow plug (R18) switches on and the flame monitor (B96) monitors the start-up attempt.

5.1 The flame monitor signals within the 85 s start-up attempt: "hot" = new flame formation and thereby continuous combustion.

-----------------------------------------------------------------------------------------

5.2 After expiration of the starting attempt of 85 s the flame monitor signals: "cold" = no flame formation and therefore no continuous combustion.

 The heater booster control module (A75) starts a malfunction shut-off.

 The glow plug (R18), the fuel metering pump (M54) and the heater blower immediately switch off.

 The shut-off delay for cooling the heater and for purging the combustion chamber starts for approx. 130 s. During the shut-off delay the combustion air blower operates at partial load for approx. 35 s and at full load for approx.
95 s.

 The shut-off delay is completed. The combustion air blower (M44) switches off.

 After overheating or flame interruption eliminate the cause of the malfunction and reset the heater by switching off and back on.

-----------------------------------------------------------------------------------------

Defective coolant temperature recognition

The coolant temperature recognition is monitored internally and permanently by the heater booster control module (A75).

1 The heater is operating at partial load or full load.

2 The control module recognizes a malfunction in the coolant temperature recognition when the temperature signal has exceeded the temperature recognition range.

3 The control module actuates a malfunction shut-off to protect the heater.

4 The fuel metering pump (M54) switches off and the combustion is interrupted .

5 The shut-off delay for cooling the heater and for purging the combustion chamber starts for approx. 130 s. The combustion air blower operates at partial load for approx. 35 s and at full load for approx. 95 s.

6 The shut-off delay is completed. The combustion air blower (M44) switches off.

 Eliminate the cause of the malfunction and reset the heater by switching off and back on.