Functional Description; Switch On; Heating Operation; Switch Off - Webasto DBW 2010 Service And Repair Manual

DBW 2010/2020/300 COOLANT HEATERS

3. FUNCTIONAL DESCRIPTION

3.1 S ON
WITCH
Upon switching on the Webasto heater, the operation
indicator lamp (A) comes on, the heater motor (C) and
the coolant circulating pump (B) begin to run. After
about 10 - 25 seconds, the solenoid valve (E) opens and
fuel is sprayed into the combustion chamber. At the
same time, the electronic ignition unit (D) produces high
voltage (8000V) and the fuel - air mixture in the
combustion chamber is ignited by the spark on the
ignition electrodes. The flame is detected by the flame
detector (F), then the electronic ignition unit stops
producing high voltage and combustion continues on its
own (spark on electrodes is required only to ignite the
flame). At this time the heater is working and produces
heat.
3.2 H O
EATING PERATION
After reaching operating temperature the control unit in
conjunction with the temperature control thermostat
takes over to provide controlled operation by activation
and deactivation of the burner in order to maintain a
nearly constant temperature of the heat exchanger
(coolant).
The heating operation is terminated as soon as the upper
operating point on the temperature control thermostat is
exceeded.
A. Green light: operation
indicator, control thermostat
B. Coolant circulation pump,
negative heater
C. Heater motor
D. Electronic ignition unit
E. Fuel solenoid valve
F. Flame detector
G. Control thermostat
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The heater now starts the control idle period. Heater
operation is resumed when the temperature drops below
the lower operating point of the temperature control
thermostat.
C
A rise in temperature above the upper operating point
makes the solenoid valve in the fuel pump shut off the
fuel supply initiating the run-down. The flame
extinguishes, the combustion air fan and the circulation
pump however continue their operation. After
approximately 150 seconds run-down is completed with
deactivation of the combustion air fan.
The circulation pump remains in operation during the
control idle period. The operating indicator light also
remains on.
3.3 S
Switching off the heater stops combustion. The
operating indicator light remains on and run-down
commences. The combustion air fan and circulation
pump are deactivated after approximately 150 seconds.
The operating indicator light goes out to indicate the
heater is now fully off.
Reactivation of the heater during run-down is permitted.
The burner immediately resumes operation after the run-
up time.
1 3
2 4
A
B
C
D
E
F
G
10 - 25s 5 - 25s
8 9

1. Switch on

2. Start
3. Combustion
4. Control pause starts
5. Control pause ends
19
FUNCTIONAL DESCRIPTION
ONTROL IDLE PERIOD
O
WITCH FF
5
~150s 10 - 25s 5 - 25s
10 8

6. Switch off

7. Heater stops
8. Initial cycle
9. Safety delay time
10. Purge cycle
3
2
6
~150s
9 10
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