Air Conditioning
Air Conditioning
The A/C refrigerant system is a clutch-cycling orifice tube type. The system components include the following:
- A/C compressor
- Clutch and clutch field coil
- A/C condenser core
- A/C evaporator core
- Suction accumulator
- Connecting refrigerant lines
The refrigeration system operation is controlled by:
- Evaporator core orifice
- A/C cycling switch
- A/C pressure sensor
- A/C compressor pressure relief valve
The refrigerant system incorporates an A/C compressor controlled by an A/C cycling switch.
The A/C cycling switch senses the A/C suction pressure to control A/C compressor operation.
An A/C compressor pressure relief valve is installed in the A/C compressor to protect the refrigerant system against excessively high refrigerant pressures.
The A/C evaporator core orifice is installed in the condenser-to-evaporator tube to meter the liquid refrigerant into the A/C evaporator core.
A/C Compressor and Clutch Assembly
NOTE: Internal FS18 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 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 from vehicles equipped with an FS18 A/C compressor 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 compressor clutch field coil, the clutch plate 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, install a new 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.
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 Combo Cooler
The A/C condenser/transmission combo cooler has the following characteristics:
- It 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 bottom portion of the cooler is separated to be used for transmission oil cooling.
A/C Evaporator Core
NOTE: The evaporator core is not separately serviceable. It is serviced only with the evaporator core housing assembly.
The A/C evaporator core is the plate/fin type.
- A mixture of refrigerant and oil enters the bottom of the A/C evaporator core through the A/C evaporator core inlet tube and moves out of the A/C evaporator core through the A/C evaporator core outlet tube.
- Air from the blower motor is cooled and dehumidified as it flows through the evaporator core fins.
A/C Evaporator Core Orifice
NOTE: A new A/C evaporator core orifice should be installed whenever a new A/C compressor is installed.
The A/C evaporator core orifice has the following characteristics:
- It is located in the evaporator core inlet tube.
- It has filter screens located on the inlet and outlet ends of the tube body.
- The inlet filter screen acts as a strainer for the liquid refrigerant flowing through the A/C evaporator core orifice.
- O-ring seals on the A/C evaporator core orifice prevent the high-pressure liquid refrigerant from bypassing the A/C evaporator core orifice.
- The A/C evaporator core orifice assembly cannot be adjusted or serviced. It must be installed as a unit.
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 one hour. If even a slight amount of positive refrigerant pressure is present in the system before repairs are carried out, a new suction accumulator should not be installed.
The suction accumulator is mounted to the RH frame rail, below the coolant degas bottle.
After entering the inlet of the suction accumulator, heavier oil-laden refrigerant contacts an internally mounted dome (which serves as an umbrella) and drips down onto the bottom of the canister.
- A small diameter oil bleed hole, in the bottom of the vapor return tube, allows the accumulated heavier liquid refrigerant and oil mixture to re-enter the compressor suction line at a controlled rate.
- As the heavier mixture passes through the small diameter liquid bleed hole, it has a second chance to vaporize and recirculate through the A/C compressor without causing compressor damage due to slugging.
- A fine mesh screened filter fits tightly around the bottom of the vapor return tube to filter out refrigerant system contaminant particles.
- A desiccant bag is mounted inside the canister to absorb any moisture which may be in the refrigerant system.
- A fitting located on the side of the suction accumulator is used to mount a serviceable low-pressure A/C charge port valve.
A/C Pressure Sensor
The PCM monitors the refrigerant system high-side pressure through the A/C pressure sensor.
- A valve depressor, located inside the threaded end of the A/C pressure sensor, presses a Schrader valve stem on the compressor discharge line portion of the compressor-to-condenser discharge line.
- The A/C pressure sensor provides a voltage that is proportional to the A/C compressor discharge pressure, which allows for the A/C compressor discharge pressure to be monitored by the PCM.
- The PCM uses this information for A/C clutch control, cooling fan control and idle speed.
- It is not necessary to recover the refrigerant to remove the A/C pressure sensor.
A/C Cycling Switch
The low-charge protection switch is used to prevent A/C compressor damage in the event of a low refrigerant charge.
- The electrical switch contacts open when the suction pressure drops below normal levels. The contacts close when the suction pressure rises.
- When the A/C cycling switch contacts open, the A/C clutch field coil is de-energized and compressor operation stops.
- The A/C cycling switch is mounted on a Schrader valve-type fitting on the top of the suction accumulator.
- A valve depressor, located inside the threaded end of the A/C cycling switch, presses in on the Schrader valve stem, allowing the suction pressure inside the suction accumulator to control the operation of the A/C cycling switch.
- It is not necessary to discharge the refrigerant system to remove the A/C cycling switch.
Spring Lock Coupling
The spring lock coupling is a refrigerant line coupling held together by a garter spring inside a circular cage.
- When the coupling is connected together, the flared end of the female fitting slips behind the garter spring inside the cage of the male fitting.
- The garter spring and cage then prevent the flared end of the female fitting from pulling out of the cage.
- The O-ring seals are green in color and are made of a special material.
- Use only the specified O-ring seals listed in the Master Parts Catalog for the spring lock coupling.
- A plastic indicator ring is used on the spring lock couplings of the A/C evaporator core to indicate, during vehicle assembly, that the coupling is connected. Once the coupling is connected, the indicator ring is no longer necessary but remains captive by the coupling near the cage opening.
- An A/C tube lock coupling clip may be used to secure the coupling but is not necessary.
A/C Slim Line Fitting
The slim line fitting is an integral part of the refrigeration line or component.
- The male and female blocks of the fitting are retained with a nut.
- An O-ring seal and a gasket are installed around the tube on the male block.
- The female and male blocks are welded to the tubes and are not adjustable.
- When correctly assembled the male and female fittings should be flush with the gasket.
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 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, 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. New 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.