Heating and A/C Operation
The purpose of the heating and A/C system is to provide heated or cooled air to the interior of the vehicle. The A/C system will also remove humidity from the interior and reduce windshield fogging. Regardless of the temperature setting, the following can affect the rate that the HVAC system can achieve the desired temperature:
- Recirculation actuator setting
- Difference between inside and desired temperature
- Blower motor speed setting
- Mode setting
When the A/C switch is pressed, an A/C request serial data message to the ECM. If the ECM determines that conditions are acceptable for A/C operation, it will ground the A/C compressor clutch relay control circuit, energizing the A/C compressor clutch relay. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch. The A/C compressor clutch will engage and the compressor will operate.
The following conditions must be met in order to activate the A/C compressor:
- Battery voltage is between 9-18 V
- Engine coolant temperature is less than 120°C (248 °F)
- Engine speed is greater than 600 RPM
- Engine speed is less than 6200 RPM
- A/C high side pressure is between 220-3100 kPa (32-450 PSI)
- Throttle position is less than 95%
- Evaporator temperature is greater than 3°C (38°F)
- ECM does not detect an unacceptable torque load
- ECM does not detect insufficient idle quality
The temperature door controls the temperature of the air entering the passenger compartment. Air entering the passenger compartment passes through the heater core and/or the evaporator core. The position of the temperature door determines how much air passes through the heater or evaporator core. As the temperature control is moved to a hotter setting, the temperature door will direct more air through the heater core. As the temperature control is moved to a cooler setting, more air will be passed through the evaporator core.