3 Functional Description
BBW 46 / DBW 46
302
NOTE
The heater may also remain in part load, full load or
control idle operation for longer periods after achieving a
balance between generation and use of heat.
Also the control sequences for full load/part load and part
load/control idle may alternate dependent on the heat
required (see functional diagram).
3.1.3 Switch Off
3.1.3.1 Heater is in Combustion Operation
– After switch off the operation indicator (H1)
extinguishes.
– Dosing pump and vehicle air fan are immediately
switched off.
– Combustion air fan immediately operates in full load.
– After flame sensor signal "dark" run-down commences
(see 3.1.2).
– After run-down also the combustion air fan is
deactivated via relay K4 and the circulation pump via
relay K2.
3.1.3.2 Heater is in Control Idle
– Circulation pump and vehicle air fan continue
operation.
3.1.4 Error Lockout
In case of malfunctions the heater including the circulation
pump automatically stop operation. The operation
indicator light H1 goes off.
3.1.4.1 Error Lockout - no Flame-up
If there is a no flame-up condition even after restart, the
control unit switches the heater off with a run-down.
3.1.4.2 Error Lockout - Flame-out (e.g. lack of fuel)
If the flame extinguishes during combustion operation and
the flame sensor B1 signals "dark", the glow plug is
activated for a maximum of 90 sec (safety period) by
means of relay K1. The heater enters full load operation.
Should no combustion be achieved, the heater will go in
error lockout with a run-down.
3.1.4.3 Error Lockout - Response of Temperature
Fuse or Limiter
An overheat condition in the heating circuit will cause the
temperature fuse F3 or the temperature limiter to respond
and interrupt dosing pump control. This stops fuel delivery
and the flame extinguishes.
For further functional sequence see 3.1.4.2.
3.1.4.4 Error Lockout - after Pre-glowing with
Defective Flame Sensor
After pre-glowing the availability of a flame sensor "bright"
signal without the combustion air fan having started
operation, will cause an error lockout.
3.1.4.5 Error Lockout - Glow Plug Filament or Glow
Plug Power Open Circuit
After switch-on and after control idle the control units
listed in 3.1.1 will sample the glow plug. A glow plug
filament or glow plug power open circuit will cause an
error lockout.
3.1.4.6 Error Lockout - Low Voltage
In case of a voltage below 9.5 V ± 0.5 V (for 12 V heaters)
or 19 V ± 1 V (for 24 V heaters) measured over a period
of 20 seconds at the control unit input will cause an error
lockout with a 60 second run-down.
3.1.4.7 Remedy
– Remove error.
– The error lockout condition is cleared by heater switch-
off and subsequent switch-on (switch-off period at
least 1 sec).
– In case of overheating replace temperature fuse (see
8.7.3) or reset temperature limiter.
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