R-134A Refrigerant System
R-134A REFRIGERANT SYSTEMCAUTION Do not add R-12 refrigerant to an A/C system that requires the use of R-134a refrigerant. Also, do not add R-134a refrigerant to an A/C system that requires the use of R-12 refrigerant. These two types of refrigerant should never be mixed. Doing so may cause damage to the A/C system.
CAUTION: R-12 refrigerant and refrigerant oil is not compatible with R-134a refrigerant and R-134a refrigerant oil. Never mix the two refrigerants or the oils.
In an effort to avoid the use of CFC refrigerants that may harm the ozone layer of the atmosphere, Ford Motor Company has introduced a new refrigerant system on all Ford vehicles that requires the use of a non-CFC based refrigerant known as R-134a. This new type of refrigerant has many of the same properties as R-12 and is similar in form and function. However, R-134a is a Hydrofluorocarbon (HFC)-based refrigerant while R-12 is a Chlorofluorocarbon (CFC)-based refrigerant. Because of the absence of chlorine in its molecular structure, the use of R-134a refrigerant will not have any harmful effects on the ozone layer of the atmosphere.
REFRIGERANT SYSTEM
The air conditioning system uses a swash plate A/C compressor, an A/C condenser core and inlet tube, a suction accumulator/drier, a A/C cycling switch, Schrader-type service access gauge port valves, and the necessary refrigerant lines. Subsequent text covering service procedures for the A/C evaporator core orifice and refrigerant lines includes illustrations of the components involved.
REFRIGERANT CONTAINMENT SWITCH - R-134A SYSTEM
A refrigerant containment switch is used on all models with air conditioning to interrupt A/C compressor operation in the event of high system discharge pressures which could result in loss of refrigerant charge. The switch is located in the discharge line between the A/C compressor and the A/C condenser core. The switch is sensitive to the discharge pressure and functions to interrupt the A/C compressor operation if the discharge pressure exceeds a setting of 2751.1-3068.2 kPa (399-445 psi). The switch is a single function switch which only controls the circuit to the A/C cycling switch.
To introduce the subject of refrigerant flow, the Refrigerant Flow Diagram illustrates the pressure changes which take place in a typical refrigerant circuit. The diagram also calls out the physical state of the refrigerant as it passes through the circuit.
When the A/C clutch field coil in the A/C clutch is energized and the A/C clutch engages and rotates the compressor drive shaft, the double-ended pistons move backward and forward in their respective cylinder bores pulling the low-pressure gas past the suction reed into the cylinder.
As each piston is forced into its respective cylinder bore, the refrigerant vapors from the suction side of the system are compressed into an increasingly smaller area, thus increasing the refrigerant vapor pressure and raising its temperature. The higher refrigerant vapor pressure now assists in seating the suction reed valve and the discharge (high pressure) reed valve as cylinder pressure exceeds the high pressure side of the system. When the compressed vapor is discharged into the high pressure side of the refrigerant system, the discharge reed valve spring pressure and the high side refrigerant pressure close and seal the reed valve, thus preventing the discharge pressure from re-entering the compressor cylinder. The A/C compressor refrigerant vapor compression cycle begins again as the pistons are pulled from their respective compressor cylinder bores by the rotating compressor shaft.
The high-pressure, high temperature compressor discharge refrigerant vapor is released into the top of the A/C condenser core, via the discharge hose. The A/C condenser core, being close to ambient temperature, causes the refrigeration vapor to condense into a liquid when heat is removed from the refrigerant vapor by ambient air passing over the fins and tubing.
Liquid refrigerant from the outlet enters the high-pressure liquid line which then flows to the inlet side of the A/C evaporator core orifice located in the inlet tube. The A/C evaporator core orifice is the refrigerant flow control device which controls refrigerant flow to the A/C evaporator core and separates the high- and low-pressure sides of the air conditioning system. The inlet filter screen of the A/C evaporator core orifice removes coarse contaminant particles, which may be present in the liquid refrigerant, before the liquid refrigerant enters the calibrated opening in the A/C evaporator core orifice. The outlet end of the A/C evaporator core orifice has a fine mesh filter with four open side slots. It is located in the body of the A/C evaporator core orifice, upstream from the filter. The side slots and filter act as a refrigerant flow noise suppressor.
The liquid refrigerant passes through the A/C evaporator core orifice tube and enters the A/C evaporator core as a cold low-pressure liquid. As airflow passes over the plate/fin sections of the A/C evaporator core, the refrigerant inside absorbs the heat and changes into a vapor.
A/C compressor suction draws the vaporized refrigerant and oil mixture into the suction accumulator/drier where the heavier oil laden vapors fall to the bottom and the lighter vapors and oil mixture continue their path to the A/C compressor via the top of the vapor return tube.
A desiccant bag, located inside the suction accumulator/drier, absorbs and retains moisture which may be circulating in the refrigeration system. The heavier oil laden refrigerant also returns to the A/C compressor through a small liquid bleed hole near the bottom of the vapor return tube. The liquid bleed hole provides a controlled second opportunity for the accumulated refrigerant and oil mixture to revaporize as it passes though the opening to re-enter the main vapor flow path to the suction side of the A/C compressor and ensures adequate oil return to the A/C compressor.