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GENERAL INFORMATION
After 30 seconds, the fuel dosing pump begins
operating and the combustion air fan operation is
suspended for 3 seconds. Subsequently, the combus-
tion air fan speed is increased in two ramps within
56 seconds to nearly full load operation. After a
stabilization phase of 15 seconds, the combustion
air fan speed is again increased in a ramp within 50
seconds to nearly full load. After reaching full load
fuel delivery, the glow plug is deactivated and the
combustion air fan operation is increased to full
load. During the subsequent 45 seconds, as well as
in normal operation, the glow plug functions as a
flame sensor to monitor the flame condition. After
all these events, the automatically controlled heat-
ing operation starts.
In case of a no flame or a flame out condition, a
restart is automatically initiated. If the no flame
condition persists, fuel delivery is stopped and the
heater enters an error lockout mode with a run-
down of the combustion air fan. This will set one or
more DTCs in the DCHA Control's memory. If six
continuous attempts to start the heater fail due to
one or more faults in the DCHA system, the heater
enters a heater lockout mode. This will set DTC
B1813 along with any other fault(s) that the DCHA
Control identified.
3.10.3.3 HEATING
During the automatically controlled heating op-
eration, when the coolant temperature reaches
76°C (169°F), the heater will switch to a part load
operation. When the coolant temperature reaches
83°C (181°F) or if the heater runs for longer than 76
minutes the heater will switch to a control idle
period. If the coolant temperature drops to 73°C
(163°F) during a control idle period, the heater will
perform a regular starting sequence into full load
operation. A drop in coolant temperature to 66°C
(151°F) during part load operation will cause the
heater to switch to a full load operation.
3.10.3.4 DEACTIVATION
For vehicles with a Manual Temperature Control
system, the DCHA will deactivate if the:
•
engine is turned off.
•
coolant temperature reaches 83°C (181°F).
•
heater runs longer than 76 minutes (for normal
automatic controlled heating operation).
•
heater reaches 5-minute timeout period (for once
per ignition cycle operation).
•
fuel tank has less than 1/8 of a tank of fuel.
•
Power switch on the A/C - Heater Control Module
is off.
•
Blend Control on the A/C - Heater Control Mod-
ule is set below 75% reheat. 5 detents
For vehicle's with a Automatic Temperature Control
system, the DCHA will deactivate if the:
•
engine speed drops below 500 rpm.
•
engine is turned off.
•
coolant temperature reaches 83°C (181°F).
•
heater runs longer than 76 minutes.
•
fuel tank has less than 1/8 of a tank of fuel.
•
Power switch on the Automatic Temperature
Control is off.
•
Comfort level is attained as determined by the
temperature setting on the Automatic Tempera-
ture Control.
When the heater is deactivated, the combustion
stops and a run-down sequence begins. During the
run-down sequence, the combustion air fan contin-
ues operation to cool down the heater. The fan is
automatically switched off after the run-down se-
quence is complete. The run-down time and the
combustion air fan speed depend on the heater
operating condition at the time of deactivation.
Run-down time is approximately 175 seconds when
deactivated in full load operation and approxi-
mately 100 seconds when deactivated in part load
operation.
3.10.4 DIAGNOSTICS
The DCHA is fully addressable with the DRBIII .
System tests include a Field Mode Test to activate
the DCHA for diagnostic testing purposes. The
DCHA Control will store up to three DTCs in its
memory. If the Controller detects a new fault in the
DCHA system, one that is not already stored in its
memory, it will clear the oldest of the three stored
DTCs, and it will store the new fault's DTC. If the
Controller detects a reoccurrence of a stored fault, it
will overwrite that fault's DTC with the most recent
occurrence.
For vehicles equipped with Automatic Tempera-
ture Control (ATC), the AC Cooldown Test will also
activate the DCHA for diagnostic testing purposes.
The AC Cooldown Test is actuated with the DRBIII.
The test checks A/C system performance based on
evaporator temperature sensor input. It also forces
the ATC to initiate a Cabin Heater Activation re-
quest when the vehicle is equipped with a Diesel
Cabin Heater Assist (DCHA). The air conditioning
related portion of this test will not run if ambient
temperature is below 12°C (53°F). However, the
forced Cabin Heater activation will occur even if the
air conditioning portion of this test fails to initiate
because test criteria was not met. The air condition-
ing related portion of this test will pass if the
evaporator temperature drops 6.7°C (20°F) within
two minutes of starting this test. Only air condition-
ing related messages display on the DRBIII after
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