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WEBASTO THERMO 300 3FUNCTIONAL DESCRIPTION
3-1
3. Functional Description
Activation and deactivation is by means of a
• switch
• timer
dependent on the type of installation.
For monitoring operation an operating indicator light is provided.
Switch off initiates the rundown procedure (see ”Switch off”).
The heaters may be
• operated with power save for reduced fuel consumption (see circuit diagram)
• equipped or retrofitted with nozzle preheating for extreme low temperatures.
3.1 Switching On
Upon switching on, an operating indicator light will illuminate.
Combustion air fan, fuel pump and circulation pump start operation. (If fitted and temperature is < 0 °C (< 32 °F)
nozzle preheating is also activated).
After approximately 12 seconds a high voltage ignition spark is generated at the electrode tips. 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 spark at the electrode tips. A photo control device detects a flame in the combustion chamber and
deactivates the ignition system (Combustion process is self-sustaining).
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.
A rise in temperature above the upper switching point makes the solenoid valve in the fuel pump shut off the fuel
supply and initiates the rundown procedure. The flame extinguishes, the combustion air fan and the circulation pump
continuing their operation. After approximately 90 seconds rundown is completed with deactivation of the combustion
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 the rundown procedure
commences.
The combustion air fan and circulation pump are deactivated after approximately 90 to 120 seconds.
Reactivation of the heater during rundown is permitted.
3.4 Power Save
With the power save feature on, the control temperatures of the heating circuit are kept low.
This results in a reduced heat radiation loss when limited heating performance is required (e.g. in heat hold
operation) and reduces fuel consumption.