Heating and A/C Operation

The purpose of the heating and A/C system is to provide heated and cooled air to the interior of the vehicle. The A/C system will also remove humidity from the interior and reduce windshield fogging. The vehicle operator can determine the passenger compartment temperature by adjusting the air temperature switch. Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve the desired temperature:

• Recirculation actuator setting
• Difference between inside and desired temperature
• Difference between ambient and desired temperature
• Blower motor speed setting
• Mode setting
• Auxiliary HVAC settings

The purpose of the heating and A/C system is to provide heated and cooled air to the interior of the vehicle. The A/C system will also remove humidity from the interior and reduce windshield fogging. The vehicle operator can determine the passenger compartment temperature by adjusting the air temperature switch. Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve the desired temperature:

• Recirculation actuator setting
• Difference between inside and desired temperature
• Difference between ambient and desired temperature
• Blower motor speed setting
• Mode setting

Obtaining proper HVAC maximum cooling operation:

1. Open the windows to allow the escape of hot interior air.
2. Press the A/C button the A/C LED will illuminate on the A/C button.
3. Set the mode switch to any of the mode settings other than A/C Max.
4. Set the fan control to the 5 or high setting.
5. Set the temperature knob to the full cold setting by turning it counterclockwise.
6. After 90 seconds, set the A/C Max mode setting to get Recirculation.
7. Close the windows.

This procedure acts as a purge of the hot passenger compartment air while allowing cool air conditioned air to fill the passenger compartment. One of the other mode settings should be selected once a desired comfort level has been achieved.

The control module makes the following actions when making a climate selection and an air temperature setting is selected:

• When the air temperature switch is placed in the warmest position, the control module commands the air temperature door to divert maximum air past the heater core.
• When the air temperature switch is placed in the coldest position, the control module commands the air temperature door to direct air to bypass the heater core.

Pressing the A/C switch engages the A/C system and illuminates the A/C switch LED. The HVAC control module sends a class 2 request signal to the powertrain control module (PCM) or engine control module (ECM). The following conditions must be met in order for the PCM/ECM to turn ON the compressor clutch:

• Evaporator temperature more than 3°C (37°F)
• PCM/ECM sent to HVAC control module A/C clutch enabled
  • A/C high side pressure is below 2979 kPa (432 psi)
  • Ambient temperature more than 40°C (40°F)
  • A/C request from the HVAC control module
  • Battery voltage between 9-16 volts

Once engaged, the compressor clutch will be disengaged for the following conditions:

• Battery voltage below 9 volts
• A/C pressure is more than 2979 kPa (432 psi)

When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.