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Operation

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 MAY RESULT IN PERSONAL INJURY OR DEATH.
- 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 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 DCHA 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 vehicles 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 time-out 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 vehicles 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 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.

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