A/C Refrigerant System Operation

Refrigerant Flow
















During stabilized conditions (air conditioning system shutdown), refrigerant system pressures are equalized on both the high and low pressure sides of the system.

When the blower motor is on and the function selector lever is in any air conditioner position, the A/C clutch field coil is energized and the clutch plate is pulled into contact with the compressor clutch pulley. The clutch plate and hub assembly then rotates the compressor shaft.

When the compressor shaft is rotated, the pistons are alternately moved back and forth with respect to their cylinder bores. As each piston is pulled through its cylinder bore, the pressure in the cylinder suddenly reduces to a pressure (or vacuum) considerably lower than the refrigerant vapor pressure on the suction side of the refrigerant system. The higher refrigerant system vapor pressure overcomes the suction reed valve spring pressure, forcing itself through the reed valve and into the lower pressure (or vacuum) area inside the compressor cylinder. The spring pressure on the reed valve closes the valve when the refrigerant system suction vapor pressure and the compressor cylinder vapor pressure are equalized.
















As each piston is forced into its respective cylinder bore, the refrigerant vapors from the suction side of the refrigerant system are compressed into a decreasingly smaller area, thus increasing the refrigerant vapor pressure and also raising the refrigerant vapor temperature. The higher refrigerant vapor pressure now assists in sealing the suction reed valve closed and also opens the discharge (high pressure) reed valve as the cylinder pressure exceeds the higher pressure side of the refrigerant system. When the compressed higher pressure and temperature refrigerant vapor is discharged into the high pressure side of the refrigerant system, the discharge reed valve spring pressure and the high side refrigerant pressure closes and seals the reed valve, thus preventing the discharge gas from entering the compressor cylinder. The compressor's refrigerant vapor compression cycle then begins again.

The high pressure and high temperature compressor discharge refrigerant gas is released into the top of the A/C condenser core, via the compressor's discharge hose. The A/C condenser core, being close to ambient temperature, causes the refrigerant vapor to condense into a liquid when heat is removed from the refrigerant by ambient air passing over the fins and tubing of the A/C condenser core.

Liquid refrigerant from the A/C condenser core exits from the bottom of the A/C condenser core and enters the high pressure liquid line and then the inlet side of the A/C condenser core. The inlet filter screen of the A/C evaporator core orifice removes coarse contaminant particulates, which may be present in the liquid refrigerant, before the liquid refrigerant enters the calibrated opening of 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 in the body, upstream from the filter. This filter removes fine contaminants and causes some of the refrigerant to exit through the non-filtered side slots. The side slots and filter act as a refrigerant flow noise suppressor.

Pressure in the A/C evaporator core is reduced as a result of the restriction at the A/C evaporator core orifice. The pressure is lowered and the liquid refrigerant passes through the A/C evaporator core orifice and enters the A/C evaporator core at a low pressure and as a cold 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.

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 refrigerant 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 through the opening to re-enter into the main vapor flow path to the suction side of the A/C compressor.

As a general observation, it is known that the more heat there is in the air, the more moisture (water vapor) the air can hold. It is also known that warm air holding its maximum vapor content will, if it is chilled, condense and form drops of water. The temperature at which this condensation occurs is called the dew point. In percentage figures, the dew point is known as 100% relative humidity. Relative humidity can be defined as the measured percentage of moisture in a given sample of air compared with the maximum amount of moisture that the same sample of air can hold at the same temperature.

The direct effect of relative humidity on driver and passenger comfort is almost common knowledge. If the humidity is low, the air has the capacity to absorb moisture up to the point where it reaches its dew point. This capacity to absorb includes the perspiration produced by the body.

When the dew point is reached, absorption capacity no longer exists. As a result, body heat causes discomfort in the form of unabsorbed perspiration.

Air conditioning does two things to cope with the problems of high heat and humidity: (1) it cools the air to a comfortable level, and (2) it lowers the relative humidity to a comfortable percentage below the dew point.


Refrigerant Systems








All Ford Motor Company vehicles currently in production offer R-134a refrigerant systems.

The label stating A/C refrigerant use in the vehicle is attached in the engine compartment so the proper service procedure and equipment can be referenced in the service manual. An R-134a refrigerant system will have gold R-134a NON-CFC tags in addition to the refrigerant charge tag.

CAUTION: If a component has been used with R-12, it cannot be used again in an R-134a system. If used in an R-134a system, It cannot be put into an R-12 system. Contamination can occur and performance can be adversely affected because each system uses a different oil designed for that system.

Individual descriptions of the components shown are not provided. They are covered in detail in the Manual A/C-Heater. Exceptions to these referrals are those parts and equipment which are most directly involved in the diagnosis of concerns, testing of system performance, and handling of refrigerant.