Air Conditioning
Air Conditioning
The A/C system components include the following:
- A/C compressor
- A/C clutch assembly
- A/C condenser/transmission oil combo cooler
- A/C evaporator core
- Receiver/drier
- Connecting refrigerant lines
- Thermostatic Expansion Valve (TXV)
The refrigerant system incorporates an A/C compressor controlled by the PCM through an A/C clutch relay. The HVAC module sends an A/C request signal over the Medium Speed Controller Area Network (MS-CAN) to the Instrument Cluster (IC) which relays the request to the PCM over the High Speed Controller Area Network (HS-CAN). An evaporator discharge air temperature sensor is used to disengage the A/C compressor clutch when the evaporator core temperature falls below 5.5°C (42°F).
The PCM commands the A/C clutch relay to turn on the A/C compressor if all of the following conditions are met:
- The HVAC module is set to a mode which provides an A/C request to the PCM via the IC.
- The evaporator discharge air temperature sensor is reading a temperature above 5.5°C (42°F).
- The A/C pressure transducer is not reading a pressure above 2,841 kPa (412 psi) in the high side of the refrigerant system.
- The A/C pressure transducer is not reading a pressure that is too low for the given ambient temperature (indicating a low refrigerant charge condition) in the high-pressure side of the refrigerant system.
- The engine coolant temperature is not excessively high.
- The PCM has not detected a Wide Open Throttle (WOT) condition.
An A/C pressure relief valve is installed in the bottom rear of the A/C compressor to protect the refrigerant system against excessively high refrigerant pressures.
Refrigerant flow into the evaporator core is metered by a TXV.
A/C Compressor and Clutch Assembly
NOTE: The internal A/C compressor components are not serviced separately. The A/C compressor is serviced only as an assembly. The A/C clutch disc and hub, A/C compressor pulley and A/C clutch field coil are serviceable.
The A/C compressor has the following characteristics:
- A non-serviceable shaft seal.
- A pressure relief valve is installed in the bottom rear of the A/C compressor to protect the refrigerant system against excessively high refrigerant pressures. The A/C pressure relief valve is a separate component and can be removed and installed separately from the A/C compressor.
- The A/C compressor uses PAG oil or equivalent. This oil contains special additives required for the A/C compressor.
- The A/C compressor oil may have some slightly dark-colored streaks while maintaining normal oil lubricant properties. This is normal for this A/C compressor because of break-in wear that can discolor the oil.
- Use the refrigerant oil adding procedure specified for this vehicle when installing a new A/C compressor.
When battery voltage is applied to the A/C compressor clutch field coil, the clutch disc and hub assembly is drawn toward the A/C clutch pulley. The magnetic force locks the clutch plate and hub assembly and the A/C clutch pulley together as one unit, causing the compressor shaft to rotate. When battery voltage is removed from the A/C compressor clutch field coil, springs in the clutch plate and hub assembly move the clutch plate away from the A/C clutch pulley.
A/C Pressure Relief Valve
NOTE: If the A/C compressor is operating within limits and the A/C pressure relief valve is venting, or if the A/C pressure relief valve is leaking around the threads, replace the A/C pressure relief valve and O-ring. If the A/C pressure relief valve still vents after it is replaced, diagnose the refrigerant system for a restriction.
An A/C pressure relief valve is incorporated in the A/C compressor as a redundant backup to the A/C pressure transducer to prevent damage to the A/C compressor and other system components by relieving unusually high system discharge pressure build-ups.
The A/C pressure relief valve is a separate component and can be replaced separately from the A/C compressor. It is necessary to recover the refrigerant before removing the A/C pressure relief valve.
A/C Condenser/Transmission Oil Combo Cooler
The A/C condenser/transmission oil combo cooler is an aluminum fin and tube design heat exchanger, located in front of the vehicle radiator. It cools compressed refrigerant gas by allowing air to pass over fins and tubes to extract heat and by condensing gas to liquid refrigerant as it is cooled.
The top portion of the A/C condenser/transmission oil combo cooler is partitioned from the refrigerant system and is used for transmission oil cooling.
Evaporator Core
The evaporator core is an aluminum plate/fin type and is located in the heater core and evaporator core housing. A mixture of refrigerant and oil enters the bottom of the evaporator core through the evaporator core inlet tube and continues out of the evaporator core through the evaporator core outlet tube. Air from the blower motor is cooled and dehumidified as it flows through the evaporator core fins.
Thermostatic Expansion Valve (TXV)
The TXV is located between the evaporator core and the TXV manifold and tube assembly at the rear of the engine compartment. The TXV provides a restriction to the flow of refrigerant from the high-pressure side of the refrigerant system and separates the low-pressure and high-pressure sides of the refrigerant system. Refrigerant entering and exiting the evaporator core passes through the TXV through 2 separate flow paths. An internal temperature sensing bulb senses the temperature of the refrigerant flowing out of the evaporator core and adjusts an internal pin-type valve to meter the refrigerant flow into the evaporator core. The internal pin-type valve decreases the amount of refrigerant entering the evaporator core at lower temperatures and increases the amount of refrigerant entering the evaporator core at higher temperatures.
Receiver Drier
NOTE: Installation of a new receiver/drier is not required when repairing the A/C system, except when there is physical evidence of contamination from a failed A/C compressor or damage to the receiver/drier. Damage to the receiver/drier includes leaks in the receiver/drier, physical damage to the receiver/drier shell or desiccant, or moisture contamination. Moisture contamination results only from a complete loss of refrigerant and equalization of the refrigerant system pressure with atmospheric pressure for a period longer than one hour. If even a slight amount of positive refrigerant pressure is present in the system before repairs are carried out, the receiver/drier should not be replaced.
The receiver/drier is mounted to the right of the radiator support. It stores high-pressure liquid after it leaves the condenser core. A desiccant bag mounted inside the receiver/drier removes any retained moisture from the refrigerant.
Evaporator Discharge Air Temperature Sensor
The evaporator discharge air temperature sensor contains a thermistor. The resistance of this thermistor varies by a specific amount based on the evaporator discharge air temperature. The HVAC module measures a voltage ratio between the reference voltage it supplies to the sensor and the sensor return voltage to determine this resistance and the associated discharge air temperature.
The evaporator discharge air temperature sensor maintains evaporator core temperature and prevents icing of the evaporator core. It does this by signaling the HVAC module to switch off the A/C request signal to the Instrument Cluster (IC) when the evaporator discharge air temperature sensor reading falls below acceptable levels. The A/C request will be switched back on when the evaporator temperature rises above acceptable levels.
The evaporator discharge air temperature sensor can be accessed from below the LH side of the instrument panel to the right of the accelerator pedal.
A/C Pressure Transducer
The A/C pressure transducer monitors the compressor discharge pressure and sends a variable voltage signal representing the pressure to the PCM. The PCM will interrupt A/C compressor operation in the event that the A/C pressure transducer indicates high system discharge pressures. It is also used to sense low charge conditions. If the pressure is below a predetermined value for a given ambient temperature, the PCM will not allow the clutch to engage.
The A/C pressure transducer is located on the compressor-to-condenser discharge line near the condenser inlet fitting. It is not necessary to recover the refrigerant before removing the A/C pressure transducer.
Service Gauge Port Valves
The high-pressure service gauge port valve is located on the receiver/drier outlet line.
The low-pressure service gauge port valve is located on the evaporator outlet line.
The fitting is an integral part of the refrigerant line or component.
- Special couplings are required for both the high-side and low-side service gauge ports.
- A very small amount of leakage will always be detectable around the Schrader-type valve with the service gauge port valve cap removed, and is considered normal. A new Schrader-type valve core can be installed if the seal leaks excessively.
- The service gauge port valve caps are used as primary seals in the refrigerant system to prevent leakage through the Schrader-type valves from reaching the atmosphere. Always install and tighten the A/C service gauge port valve caps to the correct torque after they are removed.
Refrigerant System Dye
Fluorescent refrigerant system dye is added to the refrigerant system at the factory to assist in refrigerant system leak diagnosis using a Rotunda-approved ultraviolet black light. It is not necessary to add additional dye to the refrigerant system before diagnosing leaks, even if a significant amount of refrigerant has been removed from the system. Replacement receiver/driers are shipped with a fluorescent dye "wafer" included in the desiccant bag, which will dissolve after approximately 30 minutes of continued A/C operation. It is not necessary to add dye after flushing or filtering the refrigerant system because a new receiver/drier is installed as part of the flushing or filtering procedure. Additional refrigerant system dye should only be added if more than 50% of the refrigerant system lubricant capacity has been lost due to a fitting separation or hose rupture.