The air temperature controls are divided into four primary areas:
| • | Instrument Panel - Driver Information Center (DIC) |
| • | HVAC Control Components |
| • | The Heating and Air Conditioning System |
| • | The A/C cycle |
Driver Information Center
Instrument Panel - Display
This vehicle may be equipped with a driver information center and it displays outside temperature through the I/P Cluster display. For a better understanding of the outside air temperature sensor please refer to Driver Information Center (DIC) Description and Operation.
Ambient Air Temperature Update
The Radio/IPC displays the outside air temperature value that it receives through a Low Speed GMLAN message. The scan tool has the ability to update the displayed ambient air temperature. The HVAC Manual Tech 2 shows the ambient air temperature sensor feedback voltage under Body and Accessories / Data Display / BCM. The HVAC Auto System there is a temperature reading under HVAC / Data Display / HVAC / Sensor Data. Both readings are unfiltered so it is possible that the temperature read on the tech 2 will differ from the temperature displayed on the DIC/Radio without there being a problem with the vehicle. The DIC/Radio only displays the reading being sent from the BCM. The outside air temperature value is displayed or updated under the following conditions:
Condition | Display |
|---|---|
At start up with the engine OFF more than 3 hours. | BCM initializes the OAT value to display the actual outside air temperature. |
At start up with the engine OFF less than 3 hours or anytime when started with remote start. | BCM initializes the OAT value to display the last stored temperature displayed from prior shut off. |
When the sensor reading is greater than the last stored value. Vehicle moving below 16 km/h (10 mph). | Update of temperature display will not occur. |
When the speed is between 16-53 km/h (10-33 mph). | Update of the temperature display will occur after 5 minutes. |
When the speed greater than 53 km/h (33 mph) for 3 minutes | BCM initializes the OAT value to display the actual outside air temperature. |
When the sensor reading is less than the displayed stored value. | Updates temperature display instantly. |
HVAC Control Components
HVAC Control Module
The HVAC control module is a device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The ignition 1 voltage circuits provide power to the control assembly. The control module supports the following features:
Feature | Availability |
|---|---|
Afterblow | No |
Purge | No |
Personalization | No |
Actuator Calibration | Yes |
Air Temperature Actuator
The air temperature actuator is a 5-wire bi-directional electric motor that incorporate a feedback potentiometer. Low reference, 5-volt reference, position signal, and 2 control circuits enable the actuator to operate. The control circuits use either a 0 or 12-volt value to coordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the HVAC control module grounds one of the control circuits while providing the other with 12 volts. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.
A/C Refrigerant Pressure Sensor
The A/C refrigerant pressure sensor is a 3-wire piezoelectric pressure transducer. A 5-volt reference, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0-5 volts. When the A/C refrigerant pressure is low, the signal value is near 0 volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts.
The A/C refrigerant pressure sensor prevents the A/C system from operating when an excessively high or low pressure condition exists.
Heating and A/C Operation
The purpose of the heating and A/C system is to provide the following:
| • | Heated air |
| • | Cooled air |
| • | Remove humidity from the interior of the vehicle |
| • | Reduce windshield fogging |
Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve a desired temperature:
| • | Recirculation actuator setting |
| • | Difference between inside and desired temperature |
| • | Difference between ambient and desired temperature |
| • | Blower motor speed setting |
| • | Mode setting |
The HVAC control module commands or monitors the following actions when an air temperature setting is selected.
| • | WARMEST POSITION--The air temperature actuator door position directs maximum air flow through the heater core. |
| • | COLDEST POSITION--The air temperature actuator door position directs maximum air flow around the heater core. |
The A/C system is engaged by selecting the A/C switch for the blower motor and the mode switch on the HVAC control module. The HVAC control module sends a A/C request message to the body control module (BCM) which sends a high speed serial bus message to the powertrain control module (PCM) or engine control module (ECM) for A/C compressor clutch operation. The following conditions must be met in order for the PCM or ECM to turn on the compressor clutch:
| • | HVAC control module |
| - | Evaporator temperature more than 4°C (39°F) |
| - | Control module operating range 9 and 16 volts |
| • | PCM or ECM |
| - | Engine coolant temperature (ECT) is less than 114°C (237°F) |
| - | Engine RPM is between 0 RPM and 5,000 RPM |
| - | A/C pressure is between 2997 kPa (435 psi) and 248 kPa (36 psi). |
Once engaged, the compressor clutch will be disengaged for the following conditions:
| • | Throttle position is 100 percent. |
| • | A/C pressure is more than 2997 kPa (435 psi). |
| • | A/C pressure is less than 248 kPa (36 psi). |
| • | ECT is more than 120°C (248°F). |
| • | Engine speed is more than 5,000 RPM. |
| • | Transmission shift |
| • | PCM or ECM detects excessive torque load. |
| • | PCM or ECM detects insufficient idle quality. |
| • | PCM or ECM detects a hard launch condition. |
When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.
Remote Vehicle Start HVAC Operation
When vehicle is started in remote start status, the HVAC control head settings will power up at the same settings it was at prior to shutdown. If the fan knob is left in the OFF position, the climate control system will not operate during remote start.
Engine Coolant
Engine coolant is the key element of the heating system. The engine thermostat controls the normal engine operating coolant temperature. The thermostat also creates a restriction for the cooling system that promotes a positive coolant flow and helps prevent cavitation. Coolant enters the heater core through the inlet heater hose, in a pressurized state. The heater core is located inside the HVAC module. The ambient air drawn through the HVAC module absorbs the heat of the coolant flowing through the heater core. The HVAC module distributes heated air to the passenger compartment for consistent passenger comfort. Opening or closing the HVAC module temperature door controls the amount of heat delivered to the passenger compartment. The coolant exits the heater core through the return heater hose and is recirculated back through the engine cooling system.
