Air Conditioning
AIR CONDITIONINGThe A/C refrigerant system is a clutch cycling orifice tube type. The system components are:
- 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.
- pressure cutoff switch.
The refrigerant system incorporates and 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 compressor manifold and tube assembly 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 - SC115
NOTE:
- Internal A/C compressor components are not serviced separately. The SC115 A/C compressor is serviced only as an assembly. The clutch disc and hub, the clutch pulley and bearing, and the clutch field coil are serviceable.
- Installation of a new suction accumulator is not required when repairing the air conditioning system except when there is physical evidence of system contamination from a failed A/C compressor or damage to the suction accumulator.
The SC115 A/C compressor has the following characteristics:
- Tangential mount design: 3 lugs.
- The single manifold block of the compressor manifold and tube assembly fits to the suction and discharge ports. Two O-ring seals are used for sealing.
- An eccentric bushing is driven by the shaft of the A/C compressor.
- An orbiting scroll driven by the eccentric bushing compresses the refrigerant gas against the walls of the fixed scroll.
- Single reed-type discharge valve mounted on the back of the fixed scroll. There are no suction valves.
- Non-serviceable shaft seal fully supported on both sides by bearings.
- 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 SC115 A/C compressor may have some slightly dark colored streaks while maintaining a normal oil viscosity. This is normal for this A/C compressor because of break-in wear of the scroll seals that can discolor the oil.
- Use standard oil matching procedures when installing new compressors.
The magnetic A/C clutch has the following characteristics:
- it drives the compressor shaft.
- when battery voltage is applied to the A/C compressor clutch field coil, the clutch disc and hub assembly is drawn toward the clutch pulley.
- the magnetic force locks the clutch disc and hub assembly and the 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 disc and hub assembly move the clutch plate away from the clutch pulley.
A/C Pressure Relief Valve
An A/C pressure relief valve is incorporated in the compressor manifold and tube assembly to:
- relieve unusually high refrigerant system discharge pressure buildups. For specifications regarding operating pressure(s), refer to Specifications.
- prevent damage to the A/C compressor and other system components.
- avoid total refrigerant loss by closing after the excessive pressure has been relieved.
Condenser Core
NOTE: Installation of a new suction accumulator is not required when repairing the air conditioning system except when there is physical evidence of system contamination from a failed A/C compressor or damage to the suction accumulator.
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
NOTE: Installation of a new suction accumulator is not required when repairing the air conditioning system except when there is physical evidence of system contamination from a failed A/C compressor or damage to the suction accumulator.
The evaporator core is the plate/fin type.
- A mixture of 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.
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 air conditioning system except when there is physical evidence of system contamination from a failed A/C compressor or damage to the suction accumulator.
The suction accumulator is mounted to the right of the vehicle centerline. The inlet tube of the suction accumulator attaches directly to the evaporator core outlet tube and the outlet tube of the suction accumulator attaches to the compressor manifold and tube assembly.
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 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 discharging the A/C system.
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.
- This allows 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 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 discharge the refrigerant system to remove the A/C cycling switch.
High-Pressure Cutoff Switch
The high-pressure cutoff switch is used 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 high pressure side.
- 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.
- 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 manifold and tube assembly.
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.