Part 2 of 6

Fig.14 A/C Heater Control:

A/C HEATER CONTROL
The a/c heater control is a completely electronic control head. The a/c heater system uses all electrical controls. These controls provide the vehicle operator with a number of setting options to help control the climate and comfort within the vehicle. Refer to the owner's manual in the vehicle glove box for more information on the features, use, and suggested operation of these controls.

The a/c heater control is located to the right of the instrument cluster on the instrument panel. The a/c heater control contains a rotary-type temperature control knob, a rotary-type mode control knob, a rotary-type blower motor speed knob, and push buttons for a/c compressor and rear window defogger/heated mirror operation.

The a/c heater control is fully electronic, contains the logic and control circuits for the HVAC system, and is on the J1850 data bus.

The a/c heater control cannot be repaired. If faulty or damaged, the entire unit must be replaced. The illumination lamps are available for service replacement.

A/C LOSS OF CHARGE SWITCH
The a/c loss of charge switch is located on the top of the accumulator. The switch is used to measure if refrigerant system pressure goes too low. It is not responsible for cycling the a/c compressor clutch. The switch is screwed onto an accumulator fitting that contains a Schrader-type valve, which allows the switch to be serviced without discharging the refrigerant system. The accumulator fitting is equipped with an O-ring to seal the switch connection.

The loss of charge switch is connected in series electrically with the Heater-A/C controls between ground and the Powertrain Control Module (PCM). The switch contacts open and close causing the PCM to turn the compressor clutch on and OFF. This prevents compressor operation when the system charge is low and prevents damage to the compressor. The switch opens with a pressure of 7 to 13 psi and closes when the pressure rises to 15 to 25 psi.

Fig.16 A/C Pressure Transducer:

A/C PRESSURE TRANSDUCER
This vehicle is equipped with an a/c pressure transducer. This transducer is screwed onto a fitting on the liquid line between the condenser and the high side refrigerant system service port.

The main function of the a/c pressure transducer is to disengage the compressor clutch when the refrigerant system high pressures are too high The PCM senses a voltage from the transducer and converts it to a pressure. Based on this pressure, the PCM will disengage the clutch at 460 psi and re-engage the clutch at 290 psi. The a/c heater control also uses the pressure value to operate the auto-recirculation function for improved a/c performance under extreme conditions.

AMBIENT TEMPERATURE SENSOR
Ambient air temperature is monitored by the compass mini-trip computer module through the ambient temperature sensor. The ambient temperature sensor is a variable resistor mounted to a bracket that is secured with a screw to the right side of the radiator yoke, behind the radiator grille and in front of the engine compartment.

The ambient temperature sensor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The ambient temperature sensor is a variable resistor that operates on a five-volt reference signal sent to it by the HVAC control head unit. The resistance in the sensor changes as temperature changes, changing the temperature sensor signal circuit voltage to the HVAC control head unit. Based upon the resistance in the sensor, the HVAC control head unit senses a specific voltage on the temperature sensor signal circuit, which it is programmed to correspond to a specific temperature.