This vehicle uses two systems for cabin heating. These are a heat pump system and an auxiliary heater. The systems are temperature dependent for operation. The air conditioning system in the heat pump mode is used if the ambient air temperature is between 2°C (35.6°F) and 24°C (75.2°F). Refer to Refrigeration System Description.

An overlap of 2°C (35.6°F) is built into the two heating systems to prevent constant switching between the systems when the ambient air temperature is fluctuating between 2°C (35.6°F) and 4°C (39.2°F). If the auxiliary heater is operating and the temperature rises above 4°C (39.2°F) the heater will shut off when until the temperature rises above 4°C (39.2°F). The compressor will then switch on and the heat pump system will begin operating at which time the temperature door will remain in the full hot position for 2 minutes before switching to full cold.

The auxiliary heater system uses a remote diesel fuel auxiliary heater to heat and circulate coolant through the heater core. The auxiliary heater system consists of the following components:

The auxiliary heater will operate when the ambient air temperature is below 2°C (35.6°F), the heater switch is ON, and the mode selector is in any position except OFF. The heater switch sends a signal to the HTCM and the Body Control Interface Module (BCIM) to turn the heater assembly ON and heat the coolant. The system will shut off when the ambient air temperature rises above 4°C (39.2°F).

The heater system provides the following amenities:

Outside air is drawn from the plenum at the base of the windshield. The air is then drawn into the heater module by the blower fan and forced through the heater core. The heater module mounts to the rear surface of the cowl panel beneath the instrument panel. The blower assembly mounts to the front surface of the cowl panel under the hood. Additional outside air, called ram air, is forced into the heater module by the forward movement of the vehicle.

The auxiliary heater pumps hot coolant through the core of the heater assembly. The heated coolant passing through the tubes of the heater core heats the core fins. This heat is then transferred to the air flowing past the fins. The position of the air temperature valve in the air conditioning module determines what percentage of the total air will be allowed to pass through the heater core. This determines the warmth of the total airflow that is discharged into the passenger compartment.

Air is heated as required in the heater module. The heated air is then routed through the ducts to the proper outlets for discharge into the passenger compartment. A control assembly in the instrument panel allows the operator to control the following functions coming from the heater system:

The heater module components heat the air that flows through the module. The components direct the air to the proper ducts and outlets. The heater module has two major assemblies: