Webasto Product N.A., Inc. 24 www.techwebasto.com
TROUBLESHOOTING DBW 2010/2020/300 COOLANT HEATERS
COMPONENT TEST PROCEDURES:
* INERTIA SWITCH:
All Scholastic heaters are equipped with a manual reset
inertia switch located on the tray floor near the coolant
pump. The switch has a round red diaphragm and about
the size of a 25 cent piece on top.
The purpose of this switch is to stop heater operation in
the event the vehicle is involved in an accident or receives
a strong impact shock, e.g. hitting a curb. When the
switch responds, the fan motor circuit is interrupted thus
stopping air and fuel delivery.
Always check to make certain the inertia switch has not
been tripped. Resetting is accomplished by depressing
the red diaphragm on top of the switch. You should
hear an audible click whenever the switch is reset.
MANUAL TEST RUN
OF HEATER:
A. Turn the WATER PUMP switch (4) ON
B. Turn the MOTOR switch (5) ON
C. Push and hold the FUEL SOLENOID VALVE button (7)
ON (starts fuel flow to combustion chamber)
D. Push and hold the IGNITION SPARK COIL button (6)
ON (starts electrodes sparking) until combustion has
taken place.
NOTE: Hold IGNITION SPARK COIL button (5)
ON until FLAME DETECTOR LED (3) lights or
combustion is heard, then release; in any case
do not hold button on for more than 15
seconds or damage to the coil may result.
TEST RESULTS:
1. LED (3) lights and combustion achieved
– operation normal
2. Combustion achieved but no LED (3) light
– check flame detector
3. Combustion not achieved and no LED (3) light
– check fuel nozzle
– check fuel pressure
– check for blocked fuel lines (dirt or ice)
– check ignition electrodes for damage and set
gap
E. Heater should now be in heating mode and will
continue to run until you release the fuel solenoid
valve button (7) which stops fuel flow and
extinguishes the flame immediately.
Allow the heater to continue running for
approximately 30 seconds (cool down) after which,
turn the WATER PUMP switch (4) and the MOTOR
switch (5) OFF.
Test Step Result If not
Tester connected BATTERY LED (1) unit lights up
CONTROL THERMOSTAT LED (2)
lights up
- test input voltage at control
terminals B4(+) and B2(-)
- check battery connections
- check battery voltage
- test switch/ timer
- test control thermostat on heater Normal operating range
- approx. 75 °C (167 °F) or higher
open (no heat required)
- approx. 68 °C (155 °F) or lower
closed (heat required)
Push FUEL SOLENOID VALVE button (7) several
times
clicking of solenoid should be
heard
- test temperature fuse (if equipped)
- test overheat limiter
- test solenoid valve
Push IGNITION SPARK COIL
button (6)
sparking should be heard - check electrode gap
- test ignition spark coil
Turn MOTOR switch (5) “ON“ motor should run - reset *inertia switch (Scholastic Heater Only)
- test motor
Turn WATER PUMP switch (4) “ON“ pump should run - test pump
Table 1. Test procedures and result
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