Air Conditioning
Air Conditioning
The A/C refrigerant system is a clutch cycling Thermostatic Expansion Valve (TXV) type. The system components are the following:
- A/C compressor
- A/C compressor clutch assembly
- A/C condenser core with integrated receiver/drier
- Receiver/drier desiccant cartridge
- TXV (Thermostatic Expansion Valve)
- A/C evaporator core
- Connecting refrigerant lines
The refrigeration system operation is controlled by the following:
- Evaporator temperature sensor
- A/C pressure transducer
- TXV (Thermostatic Expansion Valve)
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 Smart Junction Box (SJB) which relays the request to the PCM over the High Speed Controller Area Network (HS-CAN). An evaporator temperature sensor is used to disengage the A/C compressor clutch when the evaporator core temperature falls to a temperature near freezing.
An A/C compressor pressure relief valve is installed in the A/C compressor to protect the system against excessively high refrigerant pressures as a redundant backup to the A/C pressure transducer. A TXV (Thermostatic Expansion Valve) is used to meter the liquid refrigerant into the A/C evaporator core.
A/C Compressor and Clutch Assembly
NOTE: Internal RS20 A/C compressor components are not serviced separately. The A/C compressor is serviced only as an assembly. The clutch disc and hub, A/C compressor pulley and bearing and clutch field coil are serviceable.
The RS20 A/C compressor uses the following:
- A non-serviceable shaft seal.
- A pressure relief valve installed in the rear of the compressor to protect the refrigerant system against excessively high refrigerant pressures.
- PAG oil or equivalent. This oil contains special additives required for the A/C compressor.
- PAG oil may have some slightly dark-colored streaks while maintaining normal oil viscosity. This is normal for this A/C compressor because of break-in wear that can discolor the oil.
Use standard oil matching procedures when installing new compressors.
A/C Compressor Clutch Assembly
The magnetic A/C clutch has the following characteristics:
- The A/C clutch drives the compressor shaft.
- When battery positive voltage (B+) is applied to the A/C clutch field coil, the clutch disc and hub assembly is drawn toward the A/C clutch pulley.
- The magnetic force locks the clutch disc and hub assembly and the A/C clutch pulley together as one unit, causing the compressor shaft to rotate.
- When B+ is removed from the A/C clutch field coil, springs in the clutch disc and hub assembly move the clutch disc away from the A/C clutch pulley.
A/C Compressor 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 to prevent damage to the A/C compressor and other system components by relieving unusually high system discharge pressure buildups. For specifications regarding operating pressure(s), refer to Heating and Air Conditioning.
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 Core
The A/C condenser/power steering 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 receiver/drier is incorporated onto the LH side of the condenser core. The receiver/drier cartridge is a separate component and can be removed and installed separately from the condenser core.
A/C Evaporator Core
NOTE: If an evaporator core leak is suspected, the evaporator core must be vacuum leak tested before it is removed.
The evaporator core is an aluminum tube/fin type heat exchanger and is located in the heater core and evaporator core housing. A mixture of liquid refrigerant and oil enters the bottom of the evaporator core through the evaporator core inlet tube and then moves out of the evaporator core through the evaporator core outlet tube as a vapor. During A/C operation, airflow from the blower motor is cooled and dehumidified as it flows through the evaporator core fins.
Thermostatic Expansion Valve (TXV)
NOTE: A new TXV (Thermostatic Expansion Valve) should be installed following A/C compressor failures that produce foreign material in the system.
The TXV (Thermostatic Expansion Valve) is located at the rear of the engine compartment. The TXV (Thermostatic Expansion Valve) 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 (Thermostatic Expansion Valve) 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 cartridge is not required when repairing the A/C system, except when there is physical evidence of system contamination from a failed A/C compressor or damage to the receiver/drier cartridge. Damage to the receiver/drier cartridge includes physical damage to the receiver/drier cartridge 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 cartridge should not be replaced.
The receiver/drier is integral to the A/C condenser. It stores high-pressure liquid after it leaves the condenser core. A receiver/drier desiccant cartridge mounted inside the receiver/drier removes any moisture from the refrigerant. The receiver/drier desiccant cartridge is a separate component and can be removed and installed separately from the A/C condenser.
Evaporator Temperature Sensor
The evaporator temperature sensor contains a thermistor. The resistance of this thermistor varies by a specific amount based on the evaporator core temperature. The HVAC module measures a voltage ratio between the reference voltage it supplies to the sensor and the sensor voltage to determine this resistance and the associated evaporator core temperature.
As the evaporator core removes heat and moisture from the airflow moving through the evaporator core fins, the removed moisture condensates on the exterior of the evaporator core. The HVAC module uses input from the evaporator temperature sensor to prevent this moisture from freezing on the exterior of the evaporator core, and inhibiting airflow through the evaporator core fins. When the evaporator core temperature drops to a temperature near the freezing point of water, the HVAC module will switch off the A/C request signal to the IC (Instrument Cluster). The A/C request will be switched back on when the evaporator core temperature rises to an acceptable level.
The evaporator temperature sensor electrical connector is located outside of the heater core and evaporator core housing behind the glove compartment, with the sensor pigtail leading into the housing to the sensor probe which is inserted between the evaporator core fins.
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 compressor-to-condenser discharge line near the condenser fitting.
The low-pressure service gauge port valve is located on the evaporator-to-compressor suction line.
The fitting is an integral part of the refrigeration 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, this 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 blacklight. 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. New receiver/drier cartridges 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 cartridge 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, hose rupture or other damage.