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The temperature sensor senses the coolant tem-
perature in the heat exchanger as an electrical
resistance. This signal is sent to the control unit for
processing.
The overheat protection, controlled by the tem-
perature resistor, protects the heater against undue
operating temperatures. The overheat protection
will switch the heater off if the water temperature
exceeds 105°C (221°F).
3.10.2.6 DOSING PUMP
The dosing pump is a combined delivery, dosing,
and shut-off system for the fuel supply of the heater.
The dosing pump receives its supply of fuel from the
vehicle's fuel tank.
3.10.3 OPERATION
3.10.3.1 VENTING THE DCHA'S EXHAUST
WARNING: DO NOT OPERATE THE DCHA IN
AN ENCLOSED AREA SUCH AS A GARAGE
THAT
DOES
NOT
VENTILATION FACILITIES. ALWAYS VENT
THE DCHA's EXHAUST WHEN OPERATING
THE DCHA. FAILURE TO FOLLOW THESE
INSTRUCTIONS MAY RESULT IN PERSONAL
INJURY OR DEATH.
WARNING: ALLOW THE DCHA ASSEMBLY TO
COOL BEFORE PERFORMING A COMPONENT
INSPECTION/REPAIR/REPLACEMENT. FAILURE
TO FOLLOW THESE INSTRUCTIONS MAY
RESULT IN PERSONAL INJURY.
CAUTION: When using a powered exhaust
ventilation system, do not attach the exhaust
ventilation hose directly to the DCHA exhaust
pipe. Too much suction can prevent DCHA
operation.
•
When using a powered exhaust ventilation sys-
tem, affix the ventilation hose to the DCHA
exhaust pipe or to the vehicle in such a manor
that the end of the ventilation hose remains
approximately three inches away from the end of
the DCHA exhaust pipe.
•
When using a non-powered exhaust ventilation
system, affix the ventilation hose directly to the
DCHA exhaust pipe.
3.10.3.2 ACTIVATION
When the ignition is in Run, the FCM monitors
the PCI bus for the Cabin Heater Activation re-
quest. The Automatic or Manual Temperature Con-
trol initiates this request only when all conditions
HAVE
EXHAUST
23
GENERAL INFORMATION
for Cabin Heater activation are favorable (see be-
low). The request carries the status bit that the
FCM requires to activate its Cabin Heater Assist
Control Output. This output is a low side driver
(coming from FCM pin 15) which supplies a ground
signal to the Cabin Heater (pin 5). When the Cabin
Heater receives this ground signal input, it inter-
prets this as an activation signal. The FCM low side
driver is also capable of diagnostic sensing. The
driver will sense an open circuit when the driver is
off, and will sense a short to voltage when the driver
is on. The FCM will set DTCs for both of these types
of faults.
For vehicle's with a Manual Temperature Control
system, the DCHA will activate only:
•
when the engine is running.
•
when the coolant temperature is below 66°C
(151°F).
•
when the fuel tank has greater than 1/8 of a tank
of fuel.
•
when the Power switch on the A/C - Heater
Control Module is on.
•
when the Blend control on the A/C - Heater
Control Module is set above 90% reheat (within 2
detents of the full heat position).
•
once per ignition cycle, when the ambient tem-
perature is below 9°C (49°F), and the vehicle
speed is above 25 km/h (15.5 mph) for two min-
utes, and the Blend control on the A/C - Heater
Control Module is set anywhere from 80% to 90%
reheat (3 to 4 detents from the full heat position).
Under this circumstance, the DCHA will remain
active for five minutes unless additional input is
supplied to the DCHA.
•
when the Front Control Module (FCM) sees the
Cabin Heater Activation request that is bussed
from the A/C - Heater Control Module.
For vehicle's with a Automatic Temperature Control
system, the DCHA will activate only when the:
•
VIN indicates that the vehicle has a diesel engine
•
vehicle's odometer reads more than 5 miles.
•
engine speed is above 500 rpm.
•
coolant temperature is below 66°C (151°F).
•
fuel tank has greater than 1/8 of a tank of fuel.
•
Power switch on the Automatic Temperature
Control is on.
•
Driver Temperature Control on the Automatic
Temperature Control is set above 22°C (72°F).
•
Front Control Module (FCM) sees the Cabin
Heater Activation request that is bussed from the
Automatic Temperature Control.
When the DCHA starting sequence begins, the
glow plug and the combustion air fan are activated.
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