Description

Heating and Ventilation

NOTE:
A = Hardwired; N = Medium speed CAN (controller area network) bus; O = LIN (local interconnect network) bus.









PRINCIPLES OF OPERATION
Operation of the heating and ventilation system is controlled by the ATC (automatic temperature control) module. For additional information, refer to Control Components Control Components
The system can be operated in automatic or manual mode, with temperature settings selected using the switches on the integrated control panel and, on four zone systems, the rear climate control panel.
When the engine is running, coolant is constantly circulated through the heater core by the engine coolant pump.
The blower is supplied with power from the blower relay on the RJB (rear junction box) and connected to ground via the blower control module. The blower control module regulates the voltage across the blower motor to control blower speed. The voltage set by the blower control module is controlled by a PWM (pulse width modulation) signal from the ATC (automatic temperature control) module. The ATC (automatic temperature control) module uses a feedback signal from the blower control module to monitor blower speed.

HEATER ASSEMBLY









The heater assembly controls the temperature and flow of air supplied to the air distribution ducts. The heater assembly is mounted on the vehicle centerline, between the instrument panel and the engine bulkhead. The heater assemblies on two and four zones systems are the same.
The heater assembly consists of a casing that contains an A/C (air conditioning) evaporator, a heater core, distribution control doors and temperature control doors. On 3.0L diesel vehicles, the heater assembly also contains a PTC (positive temperature coefficient) electric booster heater.
Mounted on the heater casing are 13 stepper motors. Each of the stepper motors is connected to either a distribution control door or a temperature control door.

NOTE:
The stepper motors are particularly susceptible to low voltage and a range of stepper motor DTC (diagnostic trouble code)'s are likely due to low voltage at engine crank. Only take note of these if it is a permanent fault that recurs persistently.
The evaporator is part of the A/C (air conditioning) system. For additional information, refer to Air Conditioning Air Conditioning
The heater core provides the heat source to warm the air supplied to the passenger compartment. The heater core is an aluminum two pass, fin and tube heat exchanger, and is installed across the width of the heater housing. Two aluminum tubes attached to the heater core extend through the engine bulkhead and connect to the engine cooling system.

AIR INLET DUCT









The air inlet duct connects the fresh air inlet in the engine bulkhead to the heater assembly. The air inlet duct is installed behind the instrument panel on the passenger side.
The air inlet duct consists of a casing that contains a pollen filter, an air inlet door, a blower and a blower control module. A recirculation air inlet is incorporated into the casing. A servo motor mounted on the casing is connected to the air inlet door, to allow selection between fresh and recirculated air.
The pollen filter is installed in the fresh air inlet of the air inlet duct. A cover on the underside of the air inlet duct allows access for replacement of the pollen filter.
The blower regulates the volume of air flowing through the air inlet duct to the heater assembly. The blower consists of an open hub, centrifugal fan and an electric motor.
The blower control module regulates the power supply to the blower motor. The blower control module is installed in the air inlet duct downstream of the blower, where any heat generated during operation is dissipated by the air flow.

VENTILATION OUTLETS





The ventilation outlets allow the free flow of air through the passenger compartment. The outlets are installed in the LH (left-hand) and RH (right-hand) rear quarter panels, behind the rear bumper. Each ventilation outlet consists of a grille covered by a soft rubber flaps, and is effectively a non-return valve. The flaps open and close automatically depending on the pressure differential between the air inside and outside the vehicle.