Cabin Heater

NOTE: The Cabin Heater, also known as the Diesel Cabin Heater Assist (DCHA), will be referred to as the DCHA throughout most of the General Information and the Diagnostic Procedures.

GENERAL SAFETY INFORMATION

WARNING:
- DO NOT OPERATE THE DCHA IN AN ENCLOSED AREA SUCH AS A GARAGE THAT DOES NOT HAVE EXHAUST VENTILATION FACILITIES. ALWAYS VENT THE DCHA's EXHAUST WHEN OPERATING THE DCHA. REFER TO VENTING THE DCHA'S EXHAUST FOR PROPER EXHAUST VENTING INSTRUCTIONS. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.
- ALLOW THE DCHA ASSEMBLY TO COOL BEFORE PERFORMING A COMPONENT INSPECTION REPAIR REPLACEMENT. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.
- ALWAYS DISCONNECT THE VEHICLE'S BATTERY PRIOR TO PERFORMING ANY TYPE OF WORK ON THE DCHA. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.
- NEVER ATTEMPT TO REPAIR THE DCHA HEATER MODULE OR ANY OF ITS INTERNAL COMPONENTS. ALWAYS PERFORM DCHA COMPONENT REPLACEMENT IN ACCORDANCE WITH THE SERVICE INFORMATION. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.

CAUTION:
- Do not actuate the DCHA Field Mode Test with the engine off. Failure to follow these instructions can result in internal damage to the DCHA Heater Module.
- Always Perform The Cabin Heater Pre-Test Prior To Performing Any Other Cabin Heater Test For The Test Result To Be Valid.

NOTE:
- Do not disconnect the vehicle's battery or the DCHA's main power-supply while the DCHA is in operation or In run-down mode. Failure to follow these instructions can result in excess emissions from the DCHA Heater Module.
- Failure to prime the Dosing Pump after draining the DCHA fuel line will prevent DCHA heater activation during the first attempt to start the heater. This will also set a Diagnostic Trouble Code (DTC) in the DCHA Control's memory. Do not perform the Dosing Pump Priming Procedure if an attempt was made to start the DCHA without priming the Dosing Pump first. This will put excess fuel in the DCHA Heater Module and cause smoke to emit from the DCHA exhaust pipe when heater activation occurs.
- Waxed fuel can obstruct the fuel line and reduce flow. Check for the appropriate winter grade fuel and replace as necessary.

COMPONENT DESCRIPTION AND OPERATION

DCHA ASSEMBLY
The DCHA is a supplemental heater designed to pre-heat the engine's coolant in order to supply the vehicle's occupants with heat prior to the engine reaching operating temperature. The DCHA assembly mounts underneath the vehicle on the left side floor pan near the front door opening. The DCHA assembly connects to the vehicle's heater hoses and has a fuel supply line that connects to the vehicle's fuel tank.

The DCHA assembly consists of a:
- combustion air fan assembly
- burner housing
- burner insert
- control unit"heat exchanger
- combustion chamber
- dosing pump

COMBUSTION AIR FAN
The combustion air fan assembly includes the:
- combustion air fan
- combustion air fan inlet
- fuel supply inlet

The combustion air fan delivers the air required for combustion from the combustion air inlet to the burner insert.

BURNER HOUSING
The burner housing includes the:
- coolant inlet
- coolant outlet
- exhaust outlet

The burner housing accommodates the burner insert and is combined with the control unit/heat exchanger as an assembly.

BURNER INSERT
The burner insert includes the:
- combustion pipe fuel cross section
- glow plug/flame sensor

Inside the burner insert, fuel is distributed across the combustion-pipe fuel cross section. Combustion of the fuel/air mixture takes place within the combustion pipe to heat the exchanger. The glow plug/ flame sensor, located in the burner insert, ignites the fuel/air mixture during heater start up. After heater start up, the glow plug/flame sensor operates in the flame sensor function. The glow plug/flame sensor is an electrical resistor by design, and is located in the burner insert opposite the flame side.

CONTROL UNIT/HEAT EXCHANGER
The control unit/heat exchanger includes the:
- control unit
- temperature sensor
- overheat protection
- heat exchanger
- connector terminal

The control unit controls and monitors combustion operation. The control unit is ventilated by means of a ventilation hose routed from the combustion air collector compartment of the burner. The heat exchanger transfers the heat generated by combustion to the coolant circuit. The control unit/ heat exchanger and the burner housing are an assembly and must not be disassembled.

The temperature sensor senses the coolant temperature in the heat exchanger as an electrical resistance. This signal is sent to the control unit for processing.

The overheat protection, controlled by the temperature 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).

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.

OPERATION

VENTING THE DCHA'S EXHAUST

WARNING:
- DO NOT OPERATE THE DCHA IN AN ENCLOSED AREA SUCH AS A GARAGE THAT DOES NOT HAVE EXHAUST VENTILATION FACILITIES. ALWAYS VENT THE DCHA's EXHAUST WHEN OPERATING THE DCHA. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.
- ALLOW THE DCHA ASSEMBLY TO COOL BEFORE PERFORMING A COMPONENT INSPECTION/REPAIR/REPLACEMENT. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.

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 system, 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 DC.~ exhaust pipe.

ACTIVATION
When the ignition is in Run, the FCM monitors the PCI bus for the Cabin Heater Activation request. The Automatic or Manual Temperature Control initiates this request only when all conditions for Cabin Heater activation are favorable (see below). 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 interprets 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 temperature is below 9° C (49° F), and the vehicle speed is above 25 km/h (15.5 mph) for two minutes, 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. After 30 seconds, the fuel dosing pump begins operating and the combustion air fan operation is suspended for 3 seconds. Subsequently, the combustion 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 heating 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 rundown 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.

HEATING
During the automatically controlled heating operation, 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.

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 Module 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 83CC (181cF).
- 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 Temperature Control.

When the heater is deactivated, the combustion stops and a run-down sequence begins. During the run-down sequence, the combustion air fan continues operation to cool down the heater. The fan is automatically switched off after the run-down sequence 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 approximately 100 seconds when deactivated in part load operation.

DIAGNOSTICS
The DCHA is fully addressable with the DRB Ill�. 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 Temperature 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 request 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 conditioning 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 conditioning related messages display on the DRBIII(R) after running this test. These messages will clear after paging back out of this test. Therefore, it is important to note all of the AC Cooldown test messages before doing so. Running the AC Cooldown test will cause the DELAY and Snow/lake VF segments on the ATC to flash for 162 seconds. If the air conditioning portion of this test fails, the DELAY and Snowflake VF segments will continue to flash until the vehicle is driven more than three miles.