A/C Cycle through Auxiliary A/C Operation
The air temperature controls are divided into 11 areas:^ HVAC Control Components
^ Heating
^ Air Conditioning
^ Automatic Operation
^ Engine Coolant
^ A/C Cycle
^ Auxiliary HVAC Combinations
^ Automatic Auxiliary HVAC System
^ Manual Auxiliary HVAC W/O CF5
^ Manual Auxiliary HVAC W/CF5
^ Manual Auxiliary W/C36 or C69 Only
HVAC Control Components
The describes the some components of the HVAC system. It includes control modules, actuators and sensors which effect HVAC system operation.
A/C Cycle
Refrigerant is the key element in an air conditioning system. R-134a is presently the only EPA approved refrigerant for automotive use. R-134a is an very low temperature gas that can transfer the undesirable heat and moisture from the passenger compartment to the outside air.
The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure on the vapor refrigerant. Compressing the refrigerant also adds heat to the refrigerant. The refrigerant is discharged from the compressor, through the discharge hose, and forced to flow to the condenser and then through the balance of the A/C system. The A/C system is mechanically protected with the use of a high pressure relief valve. If the high pressure switch were to fail or if the refrigerant system becomes restricted and refrigerant pressure continued to rise, the high pressure relief will pop open and release refrigerant from the system.
Compressed refrigerant enters the condenser in a high temperature, high pressure vapor state. As the refrigerant flows through the condenser, the heat of the refrigerant is transferred to the ambient air passing through the condenser. Cooling the refrigerant causes the refrigerant to condense and change from a vapor to a liquid state.
The condenser is located in front of the radiator for maximum heat transfer. The condenser is made of aluminum tubing and aluminum cooling fins, which allows rapid heat transfer for the refrigerant. The semi-cooled liquid refrigerant exits the condenser and flows through the liquid line, to the orifice tube. The orifice tube is located in the liquid line between the condenser and the evaporator. The orifice tube is the dividing point for the high and the low pressure sides of the A/C system. As the refrigerant passes through the orifice tube, the pressure on the refrigerant is lowered. Due to the pressure differential on the liquid refrigerant, the refrigerant will begin to vaporize at the orifice tube. The orifice tube also meters the amount of liquid refrigerant that can flow into the evaporator.
Refrigerant exiting the orifice tube flows into the evaporator core in a low pressure, liquid state. Ambient air is drawn through the HVAC module and passes through the evaporator core. Warm and moist air will cause the liquid refrigerant boil inside of the evaporator core. The boiling refrigerant absorbs the moisture and heat from the ambient air. The refrigerant exits the evaporator through the suction line and back to the compressor, in a vapor state, and completing the A/C cycle of heat removal. At the compressor, the refrigerant is compressed again and the cycle of heat removal is repeated.
The conditioned air is distributed through the HVAC module for passenger comfort. The heat and moisture removed from the passenger compartment will also change form, or condense, and is discharged from the HVAC module as water.
A/C Cycle with Auxiliary
The auxiliary A/C system operates from the vehicles primary A/C system. The front or primary A/C system must be ON to allow the rear A/C system to function.
Refrigerant is the key element in an air conditioning system. R-134a is presently the only EPA approved refrigerant for automotive use. R-134a is an very low temperature gas that can transfer the undesirable heat and moisture from the passenger compartment to the outside air.
The A/C system used on this vehicle is a non cycling system. Non cycling A/C systems use a high pressure switch to protect the A/C system from excessive pressure. The high pressure switch will OPEN the electrical signal, to the compressor clutch, in the event that the refrigerant pressure becomes excessive. After the high and low side of the A/C system pressure equalize, the high pressure switch will CLOSE. Closing the high pressure switch will complete the electrical circuit to the compressor clutch. The A/C system is also mechanically protected with the use of a high pressure relief valve. If the high pressure switch were to fail or if the refrigerant system becomes restricted and refrigerant pressure continued to rise, the high pressure relief will pop open and release refrigerant from the system.
The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure on the vapor refrigerant. Compressing the refrigerant also adds heat to the refrigerant. The refrigerant is discharged from the compressor, through the discharge hose, and forced to flow to the condenser and then through the balance of the A/C system.
Compressed refrigerant enters the condenser in a high temperature, high pressure vapor state. As the refrigerant flows through the condenser, the heat of the refrigerant is transferred to the ambient air passing through the condenser. Cooling the refrigerant causes the refrigerant to condense and change from a vapor to a liquid state.
The condenser is located in front of the radiator for maximum heat transfer. The condenser is made of aluminum tubing and aluminum cooling fins, which allows rapid heat transfer for the refrigerant. The semi-cooled liquid refrigerant exits the condenser and flows through the liquid line. The liquid line flow is split and the liquid refrigerant flows to both the front or primary A/C system, and to the liquid line for the rear A/C system.
The liquid refrigerant, flowing to the rear A/C system, flows into the rear TXV. The rear TXV is located at the rear evaporator inlet. The TXV is the dividing point for the high and the low pressure sides of the rear A/C system. As the refrigerant passes through the TXV, the pressure on the refrigerant is lowered. Due to the pressure differential on the liquid refrigerant, the refrigerant will begin to boil at the expansion device. The TXV also meters the amount of liquid refrigerant that can flow into the evaporator.
Refrigerant exiting the TXV flows into the evaporator core in a low pressure, liquid state. Ambient air is drawn through the rear A/C module and passes through the evaporator core. Warm and moist air will cause the liquid refrigerant boil inside of the evaporator core. The boiling refrigerant absorbs the moisture and heat from the ambient air. The refrigerant exits the evaporator through the suction line and back to the primary A/C systems suction line. Refrigerant in the primary A/C system suction line flows back to the compressor, in a vapor state, and completes the A/C cycle of heat removal. At the compressor, the refrigerant is compressed again and the cycle of heat removal is repeated.
The conditioned air is distributed through the rear A/C module for passenger comfort. The heat and moisture removed from the rear passenger compartment will also change form, or condense, and is discharged from the rear A/C module as water.
Auxiliary HVAC Combinations
The table below represents the different auxiliary HVAC combinations. The table will help to identify the auxiliary HVAC control devices used for the different RPO configurations.
CF5: Sunroof Option
C36: Rear Auxiliary Heater System Option
C68: Single Zone Automatic HVAC System Option
C69: Rear Auxiliary Air Conditioning System Option
Manual Auxiliary: This system can be identified by the control assemblies not having Computer Climate Control on the front face plate.
Automatic Auxiliary: This system can be identified by the control modules having Computer Climate Control label on front face plate.
Air Temperature Description And Operation:
AIR TEMPERATURE
Automatic Auxiliary HVAC System
This HVAC system can be identified by the wording Computer Climate Control on the front face plate of the auxiliary control modules.
Front Auxiliary HVAC Control Assembly
The front auxiliary HVAC control assembly provides inputs to the rear auxiliary HVAC control module. It is located in the overhead console so that front seat occupants can control auxiliary HVAC operation. This assembly provides blower, air delivery mode, air temperature settings and control of which control unit will operate the auxiliary HVAC system. When the REAR position is selected, inputs from this control assembly will not be processed by the rear auxiliary HVAC control module. When OFF position is selected the auxiliary system is inoperative. The module is turned on by ignition voltage from the ignition 3 voltage circuit.
Rear Auxiliary HVAC Control Module
The rear auxiliary HVAC control module processes and controls all aspects of the automatic auxiliary HVAC system. The module has communication with the HVAC control module via 2 Keyboard Data Display (KDD) communication circuits. The system receives inputs from the auxiliary upper air temperature sensor, auxiliary lower air temperature sensor, infrared temperature sensor, and feed back signals from auxiliary mode actuator and the auxiliary air temperature actuator. Along with inputs from the front auxiliary HVAC control assembly. The outputs are the auxiliary air temperature actuator, auxiliary mode actuator, auxiliary blower motor control processor and data communication with the HVAC control module. The module is turned on by ignition voltage from the ignition 3 voltage circuit.
Auxiliary Air Temperature Actuator
The auxiliary air temperature actuator opens or closes the auxiliary air mixture door to a position to divert sufficient air past the heater core to achieve the desired vehicle temperature. The auxiliary air temperature actuator is a 5 wire actuator that incorporates a electric motor with feed back capability. The auxiliary air temperature actuator has a potentiometer integral to it. A 5-volt reference signal is sent out over the 5-volt reference circuit, through the instrument panel junction block, to the air temperature actuator. A feed back signal is provided by the air temperature door position signal circuit. The control of the auxiliary air temperature actuator is provided by the air temperature door control circuit. As the actuator moves the voltage on the door position signal circuit changes. The rear auxiliary HVAC control module monitors this signal to calculate the actual door position.
When a request of actuator position change from the rear auxiliary HVAC control module, the auxiliary air temperature door control circuit voltage is varied. A 2.5 volt signal from the rear auxiliary HVAC control module keeps the actuator stationary. A 0 volt or 5 volt signal from the rear auxiliary HVAC control module allows the actuator to rotate to a position determined by the HVAC control module. The feed back potentiometer provides the position of the actuator through a varied 5 volt signal for reference of the rear auxiliary HVAC control module.
Auxiliary Duct Air Temperature Sensors
The rear auxiliary HVAC control module receives inputs for the auxiliary air duct outlet temperature from the upper and lower auxiliary air temperature sensors. The rear auxiliary HVAC control module uses these inputs to position the auxiliary air temperature actuator to achieve and maintain the set temperature. The upper and lower auxiliary air temperature sensors are Negative Temperature Coefficient (NTC) thermistors, when the temperature of the sensor changes so does the resistance across the thermistor. When the air temperature is warm, the sensor resistance and signal voltage is low. When the air temperature is cool, the sensor resistance and signal voltage is high. Inside the rear auxiliary HVAC control module 5 volts is supplied to the auxiliary air temperature signal circuit through a fixed resistance. The fixed resistance inside the rear auxiliary HVAC control module makes the signal circuit a series circuit. As the resistance of the sensor changes, the amount of voltage it drops also changes since it is series with the fixed resistance inside the rear auxiliary HVAC control module. The rear auxiliary HVAC control module monitors the voltage drop of the circuit which is needed to calculate the air temperature. The ground for the upper and lower auxiliary air temperature sensors is provided by the low reference circuit.
The rear auxiliary HVAC control module will use a default value for the upper and lower auxiliary air temperature signal if there is a fault with the input.
The rear auxiliary HVAC control module will use this default to ensure auxiliary HVAC operation is still performed. The scan tool value will be the actual reading of the signal circuit. This means if signal circuit is shorted to a ground then the scan tool will read 0 Counts. If the signal circuit is more than 5 volts than it will read 255 Counts.
Auxiliary [1][2]Inside Air Temperature Sensor
The auxiliary inside air temperature sensor is an infrared sensor. This component is integral to the rear auxiliary HVAC control module. There is a lens on the front face plate of the rear auxiliary HVAC control module that the sensor can detect the amount of heat in the rear of the vehicle. If the sensor lens is covered the sensor can not make a proper indication of heat. The sensor does not set a DTC. The sensor helps in making the proper automatic calculations to position the auxiliary mode and temperature doors.
Auxiliary Heating Operation
The operation of the front HVAC control assembly when put into the OFF position disables the auxiliary controls. When the front HVAC control assembly is put into the REAR position the rear auxiliary HVAC control module controls the auxiliary HVAC operation. Only the rear seat occupants can control the HVAC settings. When AUTO is selected on the front auxiliary HVAC assembly, the rear auxiliary HVAC control module uses calculations based on these following components to regulate the air temperature:
^ Auxiliary [1][2]inside air temperature sensor
^ Upper auxiliary air temperature sensor
^ Lower auxiliary air temperature sensor
^ Auxiliary air temperature actuator
^ Mode actuator
The signal from the front auxiliary control assembly for auxiliary air temperature signal is a varied 12 volt signal. When a warm air request is made the signal voltage is high. When a cool air request is made the signal voltage is low.
Auxiliary A/C Operation
The operation of the front HVAC control assembly when put into the OFF position disables the auxiliary controls. When the front HVAC control assembly is put into the REAR position the rear auxiliary HVAC control module controls the auxiliary HVAC operation. Only the rear seat occupants can control the HVAC settings. When AUTO is selected on the front auxiliary HVAC assembly, the rear auxiliary HVAC control module uses calculations based on these following components to regulate the air temperature:
^ Auxiliary [1][2]inside air temperature sensor
^ Upper auxiliary air temperature sensor
^ Lower auxiliary air temperature sensor
^ Auxiliary air temperature actuator
^ Mode actuator
Manual Auxiliary HVAC W/O CF5
This system incorporates a front and rear auxiliary HVAC control assemblies that provide inputs to the auxiliary HVAC control processor.
Front Auxiliary HVAC Control Assembly
The front auxiliary HVAC control assembly provides inputs to the auxiliary HVAC control processor. It is located in the overhead console so that front seat occupants can control auxiliary HVAC operation. This assembly provides blower, air delivery mode, air temperature settings and control of which control unit will operate the auxiliary HVAC system. When the REAR position is selected, inputs from this control assembly will not be processed by the auxiliary HVAC control processor. This system does not have Class 2 communication available.
The front auxiliary HVAC control assembly receives power from the ignition 3 voltage circuit. Ground is provided by the ground circuit to a splice pack. The front HVAC control assembly will apply a ground to the rear auxiliary enable control circuit when REAR is selected. When the air temperature knob is rotated a variable resistor internal to the assembly will vary a 12 volt input. The 12 volt varied voltage is supplied to the auxiliary HVAC control processor for an auxiliary air temperature actuator position change request. This is done on the auxiliary air temperature door position signal circuit. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.
Rear Auxiliary HVAC Control Assembly
The rear auxiliary HVAC control assembly provides inputs to the auxiliary HVAC control processor. It is located in the rear headliner so that second row seat occupants can control auxiliary HVAC operation. This assembly provides blower, air delivery mode and air temperature settings. When the REAR position is selected, on the front HVAC control assembly, inputs from this control assembly will be processed by the auxiliary HVAC control processor. This system does not have Class 2 communication available.
The rear auxiliary HVAC control assembly receives power from the ignition 3 voltage circuit. Ground is provided by the ground circuit through the rear auxiliary HVAC control assembly. The front HVAC control assembly will apply a ground to the rear auxiliary enable control circuit when REAR is selected. When the air temperature knob is rotated a variable resistor internal to the assembly will vary a 12 volt input. The 12 volt varied voltage is supplied to the auxiliary HVAC control processor for an auxiliary air temperature actuator position change request. This is done on the auxiliary air temperature door position signal circuit. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.
Auxiliary HVAC Control Processor
The auxiliary HVAC control processor controls all outputs for the auxiliary HVAC system. It receives inputs from the front and rear auxiliary HVAC control assemblies. The processor positions the auxiliary air temperature actuator and auxiliary mode actuator based on these inputs. This system does not have Class 2 communication available.
The auxiliary HVAC control processor receives power from the ignition 3 voltage circuit. Ground is provided by the ground circuit through rear auxiliary HVAC control assembly and a splice pack. The system receives 12 volt varied voltage input for auxiliary air temperature change request. Then the processor creates a 12 volt varied output for control of the auxiliary air temperature actuator. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.
Auxiliary Air Temperature Actuator
The auxiliary air temperature actuator opens or closes the auxiliary air mixture door to a position to divert sufficient air past the heater core to achieve the desired vehicle temperature. The auxiliary air temperature actuator is a 3 wire actuator that incorporates a bi-directional permanent magnet electric motor. The auxiliary air temperature actuator receives power from the ignition 3 voltage circuit. Ground is provided by the ground circuit through a splice pack. The control of the air temperature actuator is provided by the auxiliary air temperature door control circuit. The auxiliary HVAC control processor provides a varied 12 volt signal to the actuator. This signal is monitored by the logic incorporated in the actuator and it will move the actuator in the desired direction when a position change is requested. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.
Auxiliary Heating Operation
When an auxiliary warm air request is made the auxiliary HVAC control processor will send a high voltage signal to the auxiliary air temperature actuator on the auxiliary air temperature door position signal circuit. This voltage signal is a varied 12 volt signal. This signal is monitored by the logic incorporated in the actuator and it will move the actuator in the desired direction when a position change is requested. The signal from the auxiliary HVAC control assemblies to the auxiliary HVAC control processor is a varied 12 volt signal. This signal, when warm air is requested, is a high voltage signal.
Auxiliary A/C Operation
When an auxiliary cool air request is made the auxiliary HVAC control processor will send a low voltage signal to the auxiliary air temperature actuator on the auxiliary air temperature door position signal circuit. This voltage signal is a varied 12 volt signal. This signal is monitored by the logic incorporated in the actuator and it will move the actuator in the desired direction when a position change is requested. The signal from the auxiliary HVAC control assemblies to the auxiliary HVAC control processor is a varied 12 volt signal. This signal, when cool air is requested, is a low voltage signal.
Manual Auxiliary HVAC W/CF5
Front Auxiliary HVAC Control Assembly
The front auxiliary HVAC control assembly is located in the front headliner. This controller controls all auxiliary HVAC operation. This assembly provides blower, air delivery mode and air temperature settings. This system does not have Class 2 communication available.
The front auxiliary HVAC control assembly receives power from the ignition 3 voltage circuit. Ground is provided by the ground circuit to a splice pack. When the air temperature knob is rotated a variable resistor internal to the assembly will vary a 12 volt input. This 12 volt varied signal is then sent to the auxiliary air temperature actuator for a change in door position. This is done on the auxiliary air temperature door position signal circuit. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.
Auxiliary Air Temperature Actuator
The auxiliary air temperature actuator opens or closes the auxiliary air mixture door to a position to divert sufficient air past the heater core to achieve the desired vehicle temperature. The auxiliary air temperature actuator is a 3 wire actuator that incorporates a bi-directional permanent magnet electric motor.
The auxiliary air temperature actuator receives power from the ignition 3 voltage circuit. Ground is provided by the ground circuit through a splice pack. The control of the air temperature actuator is provided by the auxiliary air temperature door control circuit. The auxiliary HVAC control processor provides a varied 12 volt signal to the actuator. This signal is monitored by the logic incorporated in the actuator and it will move the actuator in the desired direction when a position change is requested. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.
Auxiliary Heating Operation
When an auxiliary warm air request is made the front auxiliary HVAC control assembly will send a high voltage signal to the auxiliary air temperature actuator on the auxiliary air temperature door position signal circuit. This voltage signal is a varied 12 volt signal. This signal is monitored by the logic incorporated in the actuator and it will move the actuator in the desired direction. When a position change is requested.
Auxiliary A/C Operation
When an auxiliary cool air request is made the front auxiliary HVAC control assembly will send a low voltage signal to the auxiliary air temperature actuator on the auxiliary air temperature door position signal circuit. This voltage signal is a varied 12 volt signal. This signal is monitored by the logic incorporated in the actuator and it will move the actuator in the desired direction when a position change is requested.
Manual Auxiliary W/C36 or C69 Only
Auxiliary Heating Operation
With the C36 option there is no auxiliary A/C system. This system has only a blower motor switch to regulate air speed. It does not use a air temperature actuator or a mode actuator. The lowest blower speed will have high auxiliary duct temperature. The highest blower speed will have low auxiliary duct temperature. The slower the air travels past the auxiliary heater core the more time it has to absorb heat.
Auxiliary A/C Operation
With the C69 option there is no auxiliary heater system. This system has only a blower motor switch to regulate air speed. It does not use a air temperature actuator or a mode actuator. The lowest blower speed will have low auxiliary duct temperature. The highest blower speed will have high auxiliary duct temperature. The slower the air travels past the auxiliary evaporator core the more time the evaporator has to absorb the heat.
"For a description of the RPO Code(s) shown in this article or any of the images therein, refer to the RPO Code List found at Vehicle/Application". RPO Codes