Heating and Ventilation
Heating and Ventilation
The heating and ventilation system has the following features:
- Controls the temperature and, during A/C operation (if equipped), reduces the relative humidity of the air inside the vehicle.
- Delivers heated or cooled air to maintain the vehicle interior temperature and comfort level.
- Cooling or heating can be adjusted to maintain the desired temperature.
- System uses a reheat method to provide conditioned air to the passenger compartment.
- All airflow from the blower motor passes through the A/C evaporator core, if equipped.
- The temperature is then regulated by reheating a portion of the air and blending it with the remaining cool air to the desired temperature.
- Temperature blending is varied by the temperature blend door(s), which regulate(s) the amount of air that flows through or around the heater core, where it is then mixed and distributed. Dual-zone Electronic Automatic Temperature Control (EATC) vehicles use 2 separately actuated temperature blend doors to allow for separate temperatures to be selected for the driver and passenger sides of the vehicle. Electronic Manual Temperature Control (EMTC) vehicles use a single temperature blend door.
Heater Core
The heater core consists of fins and tubes arranged to extract heat from the engine coolant and transfer it to air passing through the heater core from the blower motor.
The heater core is located in the heater core and evaporator core housing.
Blower Motor
The blower motor draws air from the air inlet and forces it into the heater core and evaporator core housing where it is mixed and distributed. The blower motor is controlled by the blower motor switch and resistor on EMTC systems or the HVAC module and blower motor speed control on dual-zone EATC systems.
The blower motor is located on the heater core and evaporator core housing below the glove compartment.
Auxiliary Heater
An electric auxiliary heater is available as optional equipment on diesel vehicles. The auxiliary heater assembly contains the Auxiliary Heater Control Module (AHCM) and element, and is located in the airflow immediately downstream of the heater core.
Power is supplied to the electric auxiliary heater element through a fused cable connected directly to the positive battery terminal with an in-line connection at the dash panel heater tube opening. Ground is supplied to the electric auxiliary heater element through a ground cable connected directly to the negative battery terminal with an in-line connection at the dash panel heater tube opening. The electric auxiliary heater is activated by a medium speed Controller Area Network (CAN) message from the HVAC module. The Medium Speed Controller Area Network (MS-CAN) message is converted to a High Speed Controller Area Network (HS-CAN) message by the instrument cluster module and is then detected by the electric AHCM.
The auxiliary heater will be activated if all of the following conditions are met:
- The ignition switch is in the RUN/START position.
- The engine is operating at greater than 500 rpm.
- Any ON mode is selected on the HVAC module.
- The temperature setpoint is greater than 80% of the highest setting on vehicles equipped with EMTC. Dual-zone EATC vehicles use a software algorithm based on interior temperature and setpoint.
- The engine coolant temperature is less than approximately 75°C (167°F).
- No alternator faults have been recorded and the alternator is operating at less than 95% capacity.
The auxiliary heater will be deactivated if any of the following conditions exist:
- The ignition switch is in the OFF or ACC position.
- The engine coolant temperature is greater than approximately 85°C (185°F).
- An alternator fault has been detected or the alternator is operating at or above 95% capacity due to external electrical loads.
- The engine is operating at less than 500 rpm.
- The auxiliary heat request is NO from the HVAC module. If the vehicle is operating with a high alternator load, the AHCM will stabilize auxiliary heater operation at 85%. The AHCM will deactivate fully if the alternator load reaches 95% capacity.