Air Conditioning
Air Conditioning
The A/C refrigerant system is a clutch cycling orifice tube type. The system components are the following:
- A/C compressor
- A/C compressor clutch assembly
- A/C condenser core
- A/C evaporator core
- Suction accumulator
- Connecting refrigerant lines
The refrigeration system operation is controlled by the following:
- A/C evaporator core orifice
- A/C cycling switch
- High-pressure cutoff switch (5.4L and 6.8L)
- Dual-function pressure switch (6.4L diesel)
The refrigerant system incorporates an A/C compressor controlled by an A/C cycling switch. The A/C cycling switch senses pressure in the suction accumulator to control operation of the A/C compressor.
An A/C compressor pressure relief valve is installed in the A/C compressor to protect the system against excessively high refrigerant pressures. An A/C evaporator core orifice is installed in the condenser-to-evaporator line to meter the liquid refrigerant into the A/C evaporator core.
A/C Compressor and Clutch Assembly
NOTE: Internal 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 FS20 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.
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 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.
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 plate/fin type heat exchanger 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 then moves 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.
A/C Evaporator Core Orifice
NOTE: A new A/C evaporator core orifice should be installed following A/C compressor failures that produce foreign material in the system.
The evaporator core orifice is located in the condenser-to-evaporator line and can be removed and installed 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 and 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. The PCM monitors the A/C cycling switch. When the A/C cycling switch contacts are open, the PCM will disengage the A/C compressor clutch.
The A/C cycling switch is located on a Schrader-type valve fitting on the suction accumulator. It is not necessary to recover the refrigerant to remove the A/C cycling switch.
High-Pressure Cutoff Switch - 5.4L and 6.8L
The high-pressure cutoff switch is used to interrupt A/C compressor operation in the event of excessively high discharge pressure in the high-pressure side of the refrigerant system. The PCM monitors the contacts in the high-pressure cutoff switch. When the high-pressure cutoff switch is open, the PCM will disengage the A/C compressor clutch.
The high-pressure cutoff switch is located on a Schrader-type valve fitting on the compressor-to-condenser discharge line. It is not necessary to recover the refrigerant to remove the high-pressure cutoff switch.
Dual-Function Pressure Switch - 6.4L Diesel
The dual-function pressure switch includes 2 separate sets of contacts that are opened at 2 different pressures.
The first set of contacts in the dual-function pressure switch is used to interrupt A/C compressor operation in the event of excessively high discharge pressure in the high-pressure side of the refrigerant system. The PCM monitors the first set of contacts in the dual-function pressure switch. When the contacts are open, the PCM will disengage the A/C compressor clutch.
The second set of contacts in the dual-function pressure switch is used by the PCM to engage the high-speed cooling fan. When the A/C pressure rises above a preset level, the second set of contacts will close and the high-speed cooling fan will be engaged.
The dual-function pressure switch is located on a Schrader-type valve fitting on the compressor-to-condenser discharge line. It is not necessary to recover the refrigerant to remove the dual-function pressure switch.
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 suction accumulator outlet tube.
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. 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 or hose rupture.