Air Conditioning
AIR CONDITIONINGThe A/C system is a clutch cycling orifice tube type. The system components include the following:
- A/C compressor
- A/C condenser core
- A/C evaporator core
- Suction accumulator
- Connecting refrigerant lines
The A/C system operation is controlled by the following:
- Evaporator core orifice tube
- A/C cycling switch
- A/C compressor pressure relief valve
- A/C pressure transducer
The A/C system incorporates an A/C compressor controlled by the PCM through an A/C clutch relay.
The A/C cycling switch senses evaporator core pressure to control A/C compressor operation.
An evaporator core orifice tube is installed in the condenser-to-evaporator line to meter the liquid refrigerant into the evaporator core.
The A/C compressor clutch will only be engaged by the PCM if all of the following conditions are met:
- The climate control assembly or HVAC module is set to a mode which provides an A/C request to the PCM.
- The A/C cycling switch is reading an acceptable evaporator core pressure.
- The A/C pressure transducer is reading an acceptable pressure in the high side of the refrigerant system.
- The A/C compressor relay is switched to the closed position by the PCM.
- The engine coolant temperature is not excessively high.
- The PCM has not detected a wide open throttle (WOT) condition.
An A/C compressor pressure relief valve is installed in the compressor to protect the refrigerant system against excessively high refrigerant pressures.
A/C Compressor and Clutch Assembly
NOTE: Internal FS18/FS20 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 FS18/FS20 A/C compressor has the following characteristics:
- A non-serviceable shaft seal
- A pressure relief valve is installed in the rear of the compressor to protect the refrigerant system against excessively high refrigerant pressures
- 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 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
When battery voltage is applied to the A/C clutch field coil, the clutch disc and hub assembly is drawn toward the A/C compressor pulley. The magnetic force locks the clutch disc and hub assembly and the A/C compressor pulley together as one unit, causing the compressor shaft to rotate. When battery voltage is removed from the A/C clutch field coil, an annular ring in the clutch disc and hub assembly moves the clutch disc away from the A/C compressor 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 compressor pressure relief valve is installed in the compressor to relieve unusually high refrigerant system discharge pressure buildups. The compressor pressure relief valve will avoid total refrigerant loss by closing after the excessive pressure has been relieved.
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.
Condenser Core
The condenser 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.
Evaporator Core
NOTE: If an evaporator core leak is suspected, the evaporator core must be vacuum leak tested before it is removed from the vehicle.
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.
Evaporator Core Orifice
NOTE: A new evaporator core orifice should be installed whenever a new A/C compressor is installed.
The evaporator core orifice is located in the condenser-to-evaporator line, and can be removed through an access fitting. The evaporator core orifice 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.
Suction Accumulator
NOTE: Installation of a new suction accumulator 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 suction accumulator. Damage to the suction accumulator includes leaks in the suction accumulator, physical damage to the suction accumulator 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 1 hour. If even a slight amount of positive refrigerant pressure is present in the refrigerant system before repairs are carried out, the suction accumulator should not be replaced.
The suction accumulator is located at the RH rear of the engine compartment. The suction accumulator is used to prevent residual liquid refrigerant from reaching the A/C compressor after leaving the evaporator core. The suction accumulator allows the accumulated heavier liquid refrigerant and oil mixture to re-enter the compressor suction line at a controlled rate. A desiccant bag is mounted inside the canister to absorb any moisture which may be in the refrigerant system.
A/C Cycling Switch
The A/C cycling switch is used to prevent icing of the evaporator core by cycling OFF the A/C compressor clutch when the suction pressure in the low-pressure side of the refrigerant system drops below acceptable levels. When the A/C cycling switch circuit is open, the PCM will disengage the A/C compressor clutch.
The A/C cycling switch is installed on a Schrader-type valve core fitting on the suction accumulator. It is not necessary to recover the refrigerant before removing the A/C cycling switch.
A/C Pressure Transducer
The A/C pressure transducer is used by the PCM to monitor the discharge pressure in the high-pressure side of the refrigerant system. When the A/C pressure transducer is reading a discharge pressure above acceptable levels, the PCM will disengage the A/C compressor clutch.
The A/C pressure transducer is installed on a Schrader-type valve core fitting on the compressor-to-condenser discharge line. 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.
The low-pressure service gauge port valve is located on the suction accumulator.
The fitting is an integral part of the A/C 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 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. Replacement suction accumulators 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 suction accumulator 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.