Heating and A/C Operation

WARNING: This page is about a different car, the 2017 Chevrolet Spark. However, it is still accessible from the selected car via links, so may be relevant.

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 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 message to the BCM, the BCM then requests A/C operation from 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, which activate 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 excessive torque load
ECM does not detect insufficient idle quality
Outside air temperature is greater than 3°C (38°F)
Blower motor ON

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 bypass the heater core and be passed through the evaporator core.