Section 22: HEATING AND AIR CONDITIONING
PA1562
45
FIGURE 48: WEBASTO PREHEATER (104,000 BTU) 22224
The water circulation pump remains in operation
as long as the heater is operating, even in the
regulation intervals and during the delayed
cutout of the switched-off heater. The pump can
also be operated independently from the heater
by means of an appropriate circuit. The heater
can be switched on at any time, even during the
delayed cutout period. Ignition takes place once
this delay time is over.
When the heater is switched off, the fuel supply
is interrupted. The flame goes out, and at the
same time a delayed cutout of some 2.5 minutes
begins. The combustion air still flowing flushes
the remaining combustion gases out of the
chamber and cools off the hot parts on the
exhaust side of the heat exchanger, while the
water circulation pump, still running, transmits
the heat present in the heat exchanger, thus
preventing local overheats. Once the delayed
cutout time is over, both the combustion air
blower and the water circulation pump switch off
automatically. A cutout will take place in case of
any failure of the preheater.
9.8.1 Preheater Fuel Filter
The preheater fuel filter is located beside the
preheater and is accessible through engine
compartment R.H. side door.
MAINTENANCE
Replace preheater fuel filter every 50,000 miles
(80 000 km) or once a year, whichever comes
first.
9.8.2 Operation
Switch on the heater. The operation indicator
lamp comes on and the heater motor and
circulating pump begin to run. After about 10-25
seconds the solenoid valve opens and fuel is
sprayed into the combustion chamber. At the
same time, the electronic ignition unit produces
high voltage (8000 V) and the mixture of fuel
and air in the combustion chamber is ignited by
the spark on the ignition electrodes. The flame is
indicated by the flame detector, then the
electronic ignition unit stops producing high
voltage and combustion continues by itself
(spark on electrodes is required only to ignite
the flame). At this moment, the heater is working
and producing heat.
If the heater is switched off by the on/off switch,
the solenoid valve interrupts fuel supply,
combustion stops and indicator lamp turns off.
Combustion air fan still blows air, cleaning the
combustion chamber of any fumes and cooling
down the combustion chamber. Coolant
circulation pumps coolant, making a purge cycle
for approximately 2-3 minutes, thus protecting
the heater against overheating.
If the heater is not switched off by the on/off
switch, the control thermostat will switch off the
heater when coolant temperature reaches 165°
± 6°F (75° ± 3°C) and turns it on at 154° ± 9°F
(68° ± 5°C). During this time, the heater
(combustion) is off and the indication lamp and
coolant pump are on. Combustion air fan blows
air for 2-3 minutes and then turns off.
9.8.3 Preheating System Timer
The timer, located on L.H. lateral console is
used to program the starting and stopping time
of the preheating system. The system indicator
light, located on the timer, illuminates when the
system is functional.
CAUTION
The preheating system should not operate for
more than one hour before starting engine as
this could discharge batteries.
DANGER
Preheating system must not operate when
vehicle is parked inside or during fuel fill stops.
NOTE
Preheating system uses the same fuel as the
engine.
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