Air Conditioning
Air Conditioning
The A/C refrigerant system is a clutch cycling orifice tube type. The system components are the:
- A/C compressor.
- A/C compressor clutch.
- condenser core.
- evaporator core.
- suction accumulator.
- connecting refrigerant lines.
The refrigeration system operation is controlled by the:
- evaporator core orifice.
- A/C cycling switch.
- A/C pressure relief valve.
- high pressure cutoff switch.
The refrigerant system incorporates an A/C compressor controlled by an A/C cycling switch and high-pressure cutoff switch (refrigerant containment switch). The A/C cycling switch senses low-side refrigerant pressure to control A/C compressor operation and prevent evaporator core freeze-up. The high-pressure cutoff switch senses high-side refrigerant pressure to interrupt A/C compressor operation in the event of excessively high refrigerant pressure.
An A/C pressure relief valve is installed in the A/C compressor to protect the refrigerant system against excessively high refrigerant pressures.
An evaporator core orifice is installed in the evaporator core inlet tube to meter the liquid refrigerant into the 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.
NOTE: Installation of a new suction accumulator 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 suction accumulator.
The FS18 A/C compressor:
- uses a non-serviceable shaft seal.
- has a pressure relief valve installed in the rear of the compressor to protect the refrigerant system against excessively high refrigerant pressures.
- uses 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 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 B+ is removed from the A/C 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 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 Climate Control System - General Information and Diagnostics Specifications.
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 core 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.
Evaporator Core
The evaporator core is the plate/fin type and has the following characteristics:
- a mixture of liquid refrigerant and oil enters the bottom of the evaporator core through the evaporator core inlet tube and is routed so it flows through the partitioned plate/fin sections.
- refrigerant then moves out of the evaporator core through the evaporator core outlet tube as a vapor.
- during A/C operation, 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 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 evaporator core orifice prevent the high-pressure liquid refrigerant from bypassing the evaporator core orifice.
- adjustment or service cannot be made to the evaporator core orifice assembly, a new evaporator core orifice assembly 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, the suction accumulator should not be replaced.
The suction accumulator is mounted to the RH inner fender to the right of the battery.
After entering the suction accumulator inlet, 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 top of the suction accumulator is used to attach the A/C cycling switch. A long-travel Schrader-type valve stem core is installed in the fitting so that the A/C cycling switch can be removed without recovering the refrigerant.
A/C Cycling Switch
The A/C cycling switch is mounted on a Schrader-type valve 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.
- The electrical switch contacts open when the suction pressure drops. The contacts close when the suction pressure rises. For specifications regarding operating pressure(s), refer to Climate Control System - General Information and Diagnostics Specifications.
- When the A/C cycling switch contacts close, the A/C compressor clutch field coil is energized.
- When the A/C cycling switch contacts open, the A/C compressor clutch field coil is de-energized and A/C compressor operation stops.
- The A/C cycling switch will control the evaporator core pressure at a point where the plate/fin surface temperature will be maintained slightly above freezing.
- This prevents icing of the evaporator core and blockage of airflow.
- It is not necessary to recover the refrigerant to remove the A/C cycling switch.
High-Pressure Cutoff Switch
The high-pressure cutoff switch is installed on the compressor-to-condenser discharge line to interrupt A/C compressor operation in the event of high system discharge pressures.
- The high-pressure cutoff switch is mounted on a Schrader-type valve fitting on the A/C compressor discharge line.
- A valve depressor, located inside the threaded end of the high-pressure cutoff switch, presses on the Schrader valve stem.
- This allows the high-pressure cutoff switch to monitor the compressor discharge pressure.
- When the A/C compressor discharge pressure rises, the switch contacts open, disengaging the A/C compressor. When the pressure drops, the contacts close to allow operation of the A/C compressor. Refer to Climate Control System - General Information and Diagnostics Refrigerant Oil Adding.
- It is not necessary to recover the refrigerant to remove the high-pressure cutoff switch.
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. Refer to Climate Control System - General Information and Diagnostics Climate Control System.