Webasto Thermo 230 Workshop Manual - page 14
Thermo 230 / 300 / 350
3 Functional Description
301
3.
Functional Description
Activation and deactivation is by means of a
•
switch
•
timer
•
air conditioning
dependent on the type of installation.
For monitoring operation at least an operating indicator
light is provided.
Switch off releases a run-down procedure (see "Switch
off").
The heaters may be
•
operated with power save for reduced fuel
consumption (see circuit diagram)
•
equipped or retrofitted with a nozzle block preheater
for extreme low temperatures (required for operation
with PME).
Heaters with control unit 1572D only
When connecting terminal +15 or +61 the heaters may
operate in the auxiliary heating mode of operation.
3.1
Switch On
Upon switch on the operating indicator light goes on.
Combustion air fan, fuel pump and circulation pump start
operation. (If fitted and temperature is < 0 °C nozzle block
preheater is also activated).
After approximately 12 seconds (run-up time) the high
voltage igniter spark is available. Approximately 1 second
later the solenoid valve in the fuel pump opens and the
nozzle sprays fuel into the combustion chamber to be
ignited by the igniter spark. A photo control circuit
deactivates the igniter box after flame-up.
3.2
Heating Operation
After reaching operating temperature the control unit
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).
Heaters with control unit 1572D only
At a low rate of flow or in case of bad venting the control
unit sets the thresholds automatically to low values.
This prevents the temperature limiter from responding to
retarded heat.
A rise in temperature above the upper switching 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 90 seconds
(120 seconds for heaters with control unit 1572D)
run-down is completed with deactivation of the com-
bustion air fan.
The circulation pump remains in operation during the
control idle period. The operating indicator light is on.
3.3
Switch Off
Switching off the heater stops combustion. The operating
indicator light goes out and run-down commences. The
combustion air fan and circulation pump are deactivated
after approximately 90 to 120 seconds (120 seconds for
heaters with control unit 1572D).
Reactivation of the heater during run-down is permitted.
The burner immediately resumes operation after the
run-up time.
3.4
Power Save
With power save on the control temperatures of the
heating circuit are kept low. Combustion performance is
not reduced.
This results in a reduced heat radiation loss when limited
heating performance is required (e.g. in heat hold opera-
tion) cutting down fuel consumption.
3.5
Auxiliary Heating Operation (heaters
with control unit 1572D only)
When terminal +15 (ignition ON) is connected and
powered or terminal +61 (engine running), the heater ope-
rates in the auxiliary heating mode. The lower tempera-
ture threshold for reactivation of the burner after control
idle is raised above that for normal operation and is auto-
matically shifted up or down dependent on the combustion
time of the heater.
3.6
Heater Lockout (heaters with control
unit 1572D only)
After the heater has performed five start attempts due to
a malfunction or after three subsequent flame-outs the
heater enters a lockout and start attempts are suspended.
This lockout is superior to the normal error lockout.
Unlocking is performed by starting the heater and dis-
connection of the main power supply of the heater during
error run-down.