The air temperature description and operation is divided into 5 areas:

HVAC Control Assembly

The HVAC control assembly receives power from the ignition 3 voltage circuit. The HVAC control assembly incorporates three potentiometers to control mode, blower motor, and air temperature settings. The HVAC control assembly does not support personalization or class 2 communications, the assembly is not programmable.

Air Temperature Actuator

The air temperature actuator is a 3 wire bi-directional permanent magnet electric motor. The power ground and control circuits enables the actuator to operate. The HVAC control assembly controls the actuator by a variable 12 volt DC signal.

The purpose of the heater is to supply heat to the interior of the vehicle. The vehicle operator can determine the level of heat by turning the air temperature switch, located on the HVAC control assembly, to any setting. The temperature control can change the vehicle's air temperature regardless of the HVAC mode setting, heater, A/C or OFF.

When a desired temperature setting is selected, a variable resistor is used to determine the air temperature actuator position signals value. When the air temperature switch is in the warmest position the signal circuit voltage is near 12 volts. The air temperature actuator opens the air temperature door to a position to divert sufficient air past the heater core to achieve the desired vehicle temperature.

The purpose of the air conditioning (A/C) system is to provide cool air and remove humidity from the interior of the vehicle. The vehicle operator can activate the A/C system in any mode. The A/C system can operate regardless of the temperature setting, however, recirculation is available in any mode other than Defog or Defrost.

Regardless of the selected A/C mode setting, a request is made to the powertrain control module (PCM) to turn on the A/C compressor. The request is sent to the PCM through the A/C request signal circuit from the HVAC control assembly. In order for the PCM to internally ground the A/C clutch relay control circuit, the A/C high and A/C low pressure switches must be closed.

The PCM turns on the A/C compressor by providing a path to ground through the A/C compressor clutch relay control circuit for the A/C compressor clutch relay. Once the relay closes its internal switch, power from the battery is provided to the A/C compressor clutch through the A/C compressor clutch supply voltage circuit. Whenever the compressor is turned off, the A/C compressor clutch diode prevents a voltage spike from entering the vehicles electrical system. The ground circuit provides a pathway to ground for the A/C compressor clutch. The A/C compressor clutch relay control circuit is grounded internally within the PCM.

A/C Pressure Switches

The A/C system is protected by two pressure switches. The A/C high pressure switch interrupts the A/C request signal when the A/C line pressure exceeds 2896 kPa (420 psi). The A/C low pressure switch interrupts the A/C low pressure switch signal when the A/C line pressure falls below 145-172 kPa (21-25 psi). When the PCM sees an open in either signal, the A/C clutch relay control circuit is no longer grounded, thus shutting off the compressor. The low pressure switch will close when pressure reaches 262-290 kPa (38-42 psi).

A/C Pressure Switches (L65)

The A/C system is protected by 2 pressure switches. The A/C high and A/C low pressure switches interrupt the A/C request signal when the A/C line pressure exceeds or falls below a predetermined value. When the PCM sees an open in the request signal, the A/C compressor clutch relay control circuit is no longer grounded, thus shutting off the compressor.

Engine coolant is the key element of the heating system. The normal engine operating coolant temperature is controlled by the thermostat. The thermostat also creates a restriction for the cooling system that promotes a positive coolant flow and helps prevent cavitation.

Coolant enters the heater core through the inlet heater hose, in a pressurized state. The heater core is located inside the HVAC module. The heat of the coolant flowing through the heater core is absorbed by the ambient air drawn through the HVAC module. Heated air is distributed to the passenger compartment, through the HVAC module, for passenger comfort. The amount of heat delivered to the passenger compartment is controlled by opening or closing the HVAC module temperature door. The coolant exits the heater core through the return heater hose and recirculated back through the engine cooling system.