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

The control module makes the following actions when automatic operation is not selected, 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.
• When the air temperature switch is placed between the warmest and coldest positions, the control module monitors the following sensor inputs to determine the air temperature door position that diverts the appropriate amount of air past the heater core in order to achieve the desired temperature:
  • Sunload
  • Ambient temperature
  • Inside temperature

The A/C system can be engaged by pressing the A/C switch. The A/C switch will illuminate when the A/C switch is pressed to the on position. Pressing the A/C switch the control module grounds A/C request signal circuit from the powertrain control module (PCM). The following conditions must be obtained before A/C compressor engagement is allowed:

• The engine coolant temperature (ECT) is less than 121°C (250°F)
• The engine RPM is more than 550 RPM
• The A/C pressure is between 207 kPa (30 psi) and 2826 kPa (410 psi)
• The A/C request signal circuit is grounded.

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

• The throttle position is 100 percent
• The A/C pressure is more than 2826 kPa (410 psi)
• The A/C pressure is less than 207 kPa (30 psi)
• The engine coolant temperature (ECT) is more than 121°C (250°F)
• The engine speed is more than 5,500 RPM
• The transmission shift
• The PCM detects excessive torque load
• The PCM detects insufficient idle quality
• The PCM detects a hard launch condition

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