Air Temperature Description and Operation 2.2L

The air temperature controls are divided into three primary areas. The first, Heater Mode, is related to how the heater system responds when a heater mode is selected, and how the HVAC system provides the desired temperature for each setting. The second, A/C Mode, is related to how the A/C system responds when an A/C mode is selected by the vehicle operator, and how the HVAC system provides the desired temperature for each setting. The third, A/C Cycle, describes the complete A/C cycle.

The purpose of the heater is to supply heat to the interior of the vehicle. The vehicle operator can determine the level of heat by turning the temperature control, located on the HVAC control assembly, to any setting. The temperature control can change the vehicle's air temperature regardless of the HVAC mode setting, heater or A/C.

The instrument panel fuse block provides power to the air temperature actuator through the ignition 3 voltage circuit. Power and ground are provide to the HVAC control assembly by the ignition 3 voltage, ground circuits and splice pack.

When a desired temperature setting is selected, a variable resistor is used to determine the air temperature actuators setting. The resistor is located within the HVAC control assembly. Turning the temperature switch will vary the 12-volt signal. That varied 12-volt signal is sent to the servo amplifier inside the air temperature actuator on the air temperature door position signal circuit. The motor opens the air temperature door to a position to divert sufficient air past the heater core to achieve the desired vehicle temperature. The air temperature actuator is grounded through the ground circuit and splice pack.

When servicing an actuator, replace parts with the correct service parts for the actuator being serviced. The electric actuators for the manual HVAC system (C42 and C60) have a rec R on top of them. This is to differentiate from the electric actuators used on the automatic HVAC system (C68).

Engine Coolant

Engine coolant is the key element of the heating system. The normal engine operating coolant temperature is controlled by the thermostat. 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 heat of the coolant flowing through the heater core is absorbed by the ambient air drawn through the HVAC module. Heated air is distributed to the passenger compartment, through the HVAC module, for passenger comfort. The amount of heat delivered to the passenger compartment is controlled by opening or closing the HVAC module temperature door. The coolant exits the heater core through the return heater hose and recirculated back through the engine cooling system.

The purpose of the air conditioning (A/C) system is to provide cool air and remove humidity from the interior of the vehicle. The vehicle operator can activate the A/C system by activating the following modes:

The A/C system can operate regardless of the temperature setting, as long as the outside air temperature is above 3°C (37°F) degrees. If the A/C compressor clutch is turned off due to cold outside air temperatures, the compressor will not come back on until outside air temperatures reach 5°C (41°F).

Regardless of the selected A/C mode setting, a request is made to the powertrain control module (PCM) to turn on the A/C compressor. The request is made through the A/C request signal circuit from the HVAC control assembly. Power and ground are provided to the HVAC control assembly by the ignition 3 voltage, ground circuits and splice pack.

In order for the PCM to internally ground the A/C clutch relay control circuit, the request signal needs to be grounded. A 12-volt request signal is sent out over the A/C request signal circuit and grounded through the PCM when the vehicle operator makes an A/C request. When this request signal is grounded, the PCM can activate the A/C compressor clutch.

The PCM turns on the A/C compressor by providing a path to ground through the A/C clutch relay control circuit for the A/C compressor clutch relay. Power is provided to the A/C compressor clutch relay internally of the underhood fuse block. Once the relay closes its internal switch, power from the battery is provided to the A/C compressor clutch through the A/C compressor clutch supply voltage circuit. Whenever the compressor is turned off, the A/C compressor clutch diode prevents a voltage spike from burning up the compressor clutch coil. The ground circuit and underhood fuse block provides a path to ground for the compressor. The A/C clutch relay control circuit is grounded internally within the PCM.

A/C Refrigerant Pressure Sensor

The A/C system is protected by the A/C refrigerant pressure sensor. The sensors output to the PCM is variable and is dependent upon pressure inside the line. A higher pressure results in a higher voltage output. The A/C pressure is constantly monitored in order to allow the A/C compressor clutch to disengage as needed. If line pressures climb above 2826 kPa (410 psi) or fall below 207 kPa (30 psi), the PCM will turn off the A/C compressor clutch. When high side pressures drop back down between 1034 kPa (150 psi) to 1724 kPa (250 psi), the PCM will allow the A/C compressor to operate.

A 5 volt reference signal is sent out over the 5 volt reference circuit, from the PCM, to the A/C refrigerant pressure sensor. The PCM monitors the A/C pressure by sending out a separate 5 volt signal on the A/C refrigerant pressure sensor signal circuit. This circuit is how the PCM monitors HVAC pressures. Ground for the A/C refrigerant pressure sensor is provided by the low reference circuit.

Recirculation Mode

Recirculation is only available in MAX A/C. When MAX A/C mode is selected, vacuum is applied to the recirculation actuator. The force of the vacuum overcomes the spring pressure inside the actuator, which is linked to the recirculation door, into recirculation mode. This brings air from inside the vehicle instead of fresh air from the outside.

Air Temperature Actuator

The instrument panel fuse block provides power to the air temperature actuator through the ignition 3 voltage circuit. Power and ground are provided to the HVAC control assembly by the ignition 3 voltage, ground circuits and splice pack.

When a desired temperature setting is selected, a variable resistor is used to determine the air temperature actuators setting. The resistor is located within the HVAC control assembly. Turning the temperature switch will vary the 12-volt signal. That varied 12-volt signal is sent to the servo amplifier inside the air temperature actuator on the air temperature door position signal circuit. The motor opens the air temperature door to a position to divert sufficient air past the heater core to achieve the desired vehicle temperature. The air temperature actuator is grounded through the ground circuit and splice pack.

When servicing an actuator, replace parts with the correct service parts for the actuator being serviced. The electric actuators for the manual HVAC system (C42 and C60) have a rec R on top of them. This is to differentiate from the electric actuators used on the automatic HVAC system (C68).

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 a 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.

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 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 expansion device.

The expansion device (TVX or orifice tube) is located at the evaporator inlet. The expansion device is the dividing point for the high and low pressure sides of the A/C system. As the refrigerant passes through the expansion device, 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 expansion device also meters the amount of liquid refrigerant that can flow into the evaporator.

Refrigerant exiting the expansion device 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, moist air will cause the liquid refrigerant to 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.

Air Temperature Description and Operation 4.3L

The air temperature controls are divided into three primary areas. The first, Heater Mode, is related to how the heater system responds when a heater mode is selected, and how the HVAC system provides the desired temperature for each setting. The second, A/C Mode, is related to how the A/C system responds when an A/C mode is selected by the vehicle operator, and how the HVAC system provides the desired temperature for each setting. The third, A/C Cycle, describes the complete A/C cycle.

The purpose of the heater is to supply heat to the interior of the vehicle. The vehicle operator can determine the level of heat by turning the temperature control, located on the HVAC control assembly, to any setting. The temperature control can change the vehicle's air temperature regardless of the HVAC mode setting, heater or A/C.

The instrument panel fuse block provides power to the air temperature actuator through the ignition 3 voltage circuit. Power and ground are provided to the HVAC control assembly by the ignition 3 voltage, ground circuits and splice pack.

When a desired temperature setting is selected, a variable resistor is used to determine the air temperature actuators setting. The resistor is located within the HVAC control assembly. Turning the temperature switch will vary the 12-volt signal. That varied 12-volt signal is sent to the servo amplifier inside the air temperature actuator on the air temperature door position signal circuit. The motor opens the air temperature door to a position to divert sufficient air past the heater core to achieve the desired vehicle temperature. The air temperature actuator is grounded through the ground circuit and splice pack.

When servicing an actuator, replace parts with the correct service parts for the actuator being serviced. The electric actuators for the manual HVAC system (C42 and C60) have a red R on top of them. This is to differentiate from the electric actuators used on the automatic HVAC system (C68).

Engine Coolant

Engine coolant is the key element of the heating system. The normal engine operating coolant temperature is controlled by the thermostat. 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 heat of the coolant flowing through the heater core is absorbed by the ambient air drawn through the HVAC module. Heated air is distributed to the passenger compartment, through the HVAC module, for passenger comfort. The amount of heat delivered to the passenger compartment is controlled by opening or closing the HVAC module temperature door. The coolant exits the heater core through the return heater hose and recirculated back through the engine cooling system.

The purpose of the air conditioning (A/C) system is to provide cool air and remove humidity from the interior of the vehicle. The vehicle operator can activate the A/C system by activating the following modes:

The A/C system can operate regardless of the temperature setting, as long as the outside air temperature is above 3°C (37°F) degrees. If the A/C compressor clutch is turned off due to cold outside air temperatures, the compressor will not come back on until outside air temperatures reach 5°C (41°F).

Regardless of the selected A/C mode setting, a request is made to the powertrain control module (PCM) to turn on the A/C compressor. The request is made through the A/C request signal circuit from the HVAC control assembly. Power and ground are provided to the HVAC control assembly by the ignition 3 voltage, ground circuits and splice pack.

In order for the PCM to internally ground the A/C clutch relay control circuit, two separate request signals need to be grounded. A 12-volt request signal is sent out over the A/C request signal circuit, through the A/C high pressure switch, and grounded through the PCM when the vehicle operator makes an A/C request. A separate 12-volt request signal is sent out over the A/C low pressure switch signal circuit, through the A/C low pressure switch and the ground circuit. When both these request signals is grounded, the PCM can activate the A/C compressor clutch.

The PCM turns on the A/C compressor by providing a path to ground through the A/C clutch relay control circuit for the A/C compressor clutch relay. Power is provided to the A/C compressor clutch relay internally of the underhood fuse block. Once the relay closes its internal switch, power from the battery is provided to the A/C compressor clutch through the A/C compressor clutch supply voltage circuit. Whenever the compressor is turned off, the A/C compressor clutch diode prevents a voltage spike from burning up the compressor clutch coil. The ground circuit and underhood fuse block provides a path to ground for the compressor. The A/C clutch relay control circuit is grounded internally within the PCM.

A/C Pressure Switches

The A/C system is protected by two pressure switches. The A/C high pressure switch interrupts the A/C request signal when the A/C line pressures climb above 2826 kPa (410 psi). The A/C low pressure switch interrupts the A/C low pressure switch signal when the A/C line pressure fall below 207 kPa (30 psi). When the PCM sees an open in either signal, the A/C clutch relay control circuit is no longer grounded, thus shutting off the compressor. When high side pressures drop back down between 1034-1724 kPa (150-250 psi), the PCM will allow the A/C compressor to operate.

Recirculation Mode

Recirculation is only available in MAX A/C. When MAX A/C is selected, vacuum is applied to the recirculation actuator. The force of the vacuum overcomes the spring pressure inside the actuator, which is linked to the recirculation door, into recirculation mode. This brings air from inside the vehicle instead of fresh air from the outside.

Air Temperature Actuator

The instrument panel fuse block provides power to the air temperature actuator through the ignition 3 voltage circuit. Power and ground are provided to the HVAC control assembly by the ignition 3 voltage, ground circuits and splice pack.

When a desired temperature setting is selected, a variable resistor is used to determine the air temperature actuators setting. The resistor is located within the HVAC control assembly. Turning the temperature switch will vary the 12-volt signal. That varied 12-volt signal is sent to the servo amplifier inside the air temperature actuator on the air temperature door position signal circuit. The motor opens the air temperature door to a position to divert sufficient air past the heater core or evaporator to achieve the desired vehicle temperature. The air temperature actuator is grounded through the ground circuit and splice pack.

When servicing an actuator, replace parts with the correct service parts for the actuator being serviced. The electric actuators for the manual HVAC system (C42 and C60) have a red R on top of them. This is to differentiate from the electric actuators used on the automatic HVAC system (C68).

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 a 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, if the refrigerant pressure becomes excessive. After the high and the low sides of the A/C system pressure equalize, the high pressure switch will CLOSE. This completes 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 continues 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. The refrigerant is discharged from the compressor through the discharge hose, and forced through the condenser and then through the balance of the A/C system.

Compressed refrigerant enters the condenser at a high-temperature, high-pressure vapor state. As the refrigerant flows through the condenser, the heat is transferred to the ambient air passing through the condenser. Cooling 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, causing the refrigerant to vaporize at the orifice tube. The orifice tube also measures 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 to boil inside the evaporator core. The boiling refrigerant absorbs heat from the ambient air and draws moisture onto the evaporator. The refrigerant exits the evaporator through the suction line and flows back to the compressor in a vapor state, 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 condenses, and discharges from the HVAC module as water.