Section 12-03A: Air Conditioning System, Manual A/C-Heater
1996 F-150, F-250, F-350, F-Super Duty and Bronco, F-Super Duty Motorhome Chassis Workshop Manual
DESCRIPTION AND OPERATION

Refrigerant System

The following illustration shows a basic refrigerant circuit representing refrigerant changes as it passes through a cycle from compressor output to compressor input.

The illustration identifies four states in which refrigerant will exist in a closed circuit: (1) high-pressure liquid, (2) restriction, (3) low-pressure liquid and (4) low-pressure vapor. Beginning with compressor output, refrigerant moves as a high-pressure gas (7) to the A/C condenser core (19712). As it passes through the A/C condenser core, (7) the vapor condenses into a liquid.

In the course of this condensation process, the refrigerant gives up heat. This heat exchange does not alter the temperature of the refrigerant. Thus, the refrigerant continues its flow through the circuit as a high-temperature, high-pressure liquid.

The restriction called out in the illustration is an A/C evaporator core orifice (19D990) which contains a 1.575mm (0.062-inch) orifice. (This tube is color-coded red.) When the refrigerant passes through this A/C evaporator core orifice, it changes from a high- to low-pressure liquid, with a corresponding drop in temperature.

The refrigerant, upon leaving the A/C evaporator core orifice, is drawn through the circuit by compressor suction. Thus, it enters the A/C evaporator core (19860) as a low-pressure/low-temperature liquid.




ItemPart NumberDescription
119860A/C Evaporator Core (Low-Pressure Liquid In, High-Pressure Vapor Out)
219867Evaporator to Compressor Suction Line (Low-Pressure Vapor)
319703A/C Compressor (Low-Pressure Vapor In, High-Pressure Vapor Out)
419972A/C Compressor to Condenser Discharge Line (High-Pressure Vapor)
519712A/C Condenser Core (High-Pressure Vapor In, High-Pressure Liquid Out)
619835Condenser to Evaporator Tube (High-Pressure Liquid)
719D990A/C Evaporator Core Orifice (Restriction)
8Evaporator Inlet (Low-Pressure Liquid)
919C836Suction Accumulator/Drier (Low-Pressure Vapor)

The cooling of the A/C evaporator core creates a temperature differential between the A/C evaporator core and the ambient air in the A/C evaporator housing (19850). As a result of this difference, heat is absorbed from the air. Simultaneously, humidity is extracted from the air and drained onto the road surface under the vehicle. Again, the absorption of BTUs does not affect refrigerant temperature.

Refrigerant flow, after leaving the A/C evaporator core, continues through the suction accumulator/drier (19C836) where any moisture within the refrigerant system is absorbed into a desiccant bag and the more heavily oil-laden refrigerant is returned to the A/C compressor (19703) through a small bleed, liquid bleed hole, near the bottom of the aspirator tube.

The cooled, dehumidified air in the A/C evaporator case (19897) is pushed by the blower motor (18527) through the heater air plenum chamber (18471) and out through ducting to the registers in the instrument panel (04320).

Extending this basic coverage of a refrigerant circuit, the following traces refrigerant flow through actual circuit components.

When the air conditioning system is not on, refrigerant system pressures are equalized on both the high and low sides of the refrigerant system. In a system that is fully charged (saturated) and not operating, refrigerant will exist in both liquid and vapor phases.

When the function selector knob (18519) is set on A/C (MAX or NORM), MIX or DEFROST, the A/C clutch field coil (2987) is energized and the clutch plate is pulled into contact with the clutch pulley. The clutch plate and hub assembly then rotates the compressor shaft.

When the compressor shaft is rotated, the double ended pistons move backward and forward in their respective cylinder bores. As each piston is moved backward in its cylinder bore, it pulls 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 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 high-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 pressure from re-entering the compressor cylinder. The compressor's refrigerant vapor compression cycle begins again as the pistons are again pulled from their respective compressor cylinder bores by the rotating compressor shaft.

The high-pressure and high-temperature compressor discharge refrigerant vapor is released into the top of the A/C condenser core, via the A/C manifold and tube (19D734). 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 vapor by ambient air passing over the fins and tubing.

Liquid refrigerant from the outlet enters the high pressure condenser to evaporator tube (19835) and then the inlet side of the A/C evaporator core orifice located in the inlet tube. 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 of the A/C evaporator core orifice, upstream from the filter. This filter is used to reduce noise. The side slots and filter act as a refrigerant flow noise suppressor.

The liquid refrigerant passes through the A/C evaporator core orifice and enters the A/C evaporator core as a low-pressure 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.

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 that 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.

The manual air conditioning/heater refrigerant system uses a ten-cylinder swash plate A/C compressor, an A/C condenser core, an A/C evaporator core with an A/C evaporator core orifice in the inlet tube, a suction accumulator/drier with an integral drier, an A/C cycling switch (19E561), specially designed quick-release type service access gauge port valves, and the necessary refrigerant lines.

 

Service Access Gauge Port Valves

NOTE: The A/C service port fittings used in R-134a refrigerant systems are a two-piece design. The top portion of the fitting is aluminum and is threaded to the bottom part and sealed with an O-ring seal. These fittings can be serviced through the use of either the High Side A/C Fitting Socket D94L-19703-A or the Low Side A/C Fitting Socket D94L-19703-B providing the system is first discharged. Refer to Section 12-00 for discharging procedures. The valve seal is an integral part of the aluminum fitting piece which must be replaced if the seal leaks. The Schrader valve core used on R-12 systems is not used in the R-134a system.

The high-side fitting is the largest and special adapters are required to attach service equipment to both the high- and low-side system ports.

Always reinstall the A/C charging valve caps (19D702) on the service access gauge port valves after servicing the A/C system to prevent dirt from entering the valve or refrigerant system.

High-Side Service Port




 

A/C Evaporator Core

The A/C evaporator core is a plate-fin core similar to passenger car cores. The condenser to evaporator tube connects to the bottom of the A/C evaporator core and the suction accumulator/drier assembly connects to the top of the A/C evaporator core.

 

A/C Evaporator Core Orifice

The inlet tube to the A/C evaporator core is fitted with an A/C evaporator core orifice to control refrigerant flow. This A/C evaporator core orifice can be removed from the inlet tube and A/C evaporator core for replacement if it becomes necessary. However, Fixed Orifice Tube Tool D80L-19990-A or equivalent is necessary to prevent breakage when removing the A/C evaporator core orifice.

The A/C evaporator core orifice is a restriction between the high and low pressure refrigerant and meters the flow of liquid refrigerant into the A/C evaporator core. The diameter of the orifice within the A/C evaporator core orifice is 1.575mm (0.062 inch). The A/C evaporator core orifice can be identified by the RED body color and white outlet tip.

The A/C evaporator core orifice is located in the evaporator core inlet tube and has filter screens on the inlet and outlet ends of the body. The filter screens act as strainers for the liquid refrigerant flowing through the opening. O-rings on the A/C evaporator core orifice prevent the high pressure liquid refrigerant from bypassing the A/C evaporator core orifice. Adjustment or repairs cannot be made to the A/C evaporator core orifice and it must be replaced as a unit.

 

Suction Accumulator/Drier

The suction accumulator/drier is mounted to the front side of the A/C evaporator case and attaches directly to the outlet tube.

Refrigerant enters the accumulator/drier canister through the inlet tube and the heavier, oil-laden refrigerant falls to the bottom of the canister. A small diameter aspirator tube is located close to the bottom of the canister and runs to the top of the vapor return tube. This aspirator tube is covered with a filter screen and allows a small amount of the heavier liquid refrigerant and oil mixture to re-enter the A/C manifold and tube at a controlled rate. When the heavier liquid refrigerant and oil mixture enters the compressor evaporator to compressor suction line (19867), it has a second opportunity to vaporize and circulate through the A/C compressor without causing damage to the A/C compressor due to refrigerant slugging.

A desiccant bag is mounted inside the suction accumulator/drier canister to absorb any moisture that may be in the refrigerant system.

A fitting located on the side of the canister is used to attach the A/C cycling switch. A long-travel Schrader valve stem core is installed in the fitting opening to prevent refrigerant loss when the A/C cycling switch is removed.

NOTE: Replacement of the suction accumulator/drier 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/drier.

NOTE: The compressor oil may have a dark color while maintaining a normal oil viscosity. This is normal for this A/C compressor because carbon from the compressor piston rings may discolor the oil.

There is evidence of moisture in the system, such as internal corrosion of metal refrigerant lines, or the refrigerant oil is thick and dark.

When replacing the suction accumulator/drier, the procedure given here must be followed to make sure that the total oil charge in the system is correct after the new accumulator/drier is installed.

 

A/C Cycling Switch

The A/C cycling switch is mounted on a Schrader valve fitting on the side of the suction accumulator/drier assembly. A valve depressor, located inside the threaded end of the A/C cycling switch, presses in on the Schrader valve stem as the A/C cycling switch is mounted and allows the suction pressure inside the suction accumulator/drier housing to activate the A/C cycling switch. The electrical contacts will open when the suction pressure drops to 163-175 kPa (23.5-25.5 psi). They will close, activating the A/C clutch (2884), when the suction pressure rises to 276-324 kPa (40-47 psi). Lower ambient temperatures (below approximately 1°C (30°F) during cold weather seasons will also prevent A/C compressor operation, because of the pressure/temperature relationship of the refrigerant in the system.

NOTE: Temperature must drop to -4°C (25°F) to open pressure switch contacts. Contacts open at approximately -4°C (25°F) decreasing and close increasing 7.2-10°C (45-50°F).

The electrical contacts control the electrical circuit to the A/C clutch field coil. When the contacts are closed, the A/C clutch field coil is energized and the A/C clutch is engaged to drive the A/C compressor. When the contacts are open, the A/C clutch field coil is de-energized, the A/C clutch is disengaged and the A/C compressor does not operate. The A/C cycling switch, when functioning properly, will control the pressure at a point where the plate-fin surface temperature of the A/C evaporator core will be maintained slightly above freezing which prevents icing and the blockage of airflow.

 

A/C Condenser Core

The A/C condenser core is attached to the radiator support in front of the radiator (8005) with two mounting brackets at the top and bottom of the A/C condenser core. The top mounting brackets attach to the rear side of the radiator support and the lower brackets attach to the front side of the radiator support.

A/C Condenser Core Installation





ItemPart NumberDescription
119712A/C Condenser Core
219D702A/C Charging Valve Cap
3N606691-S2Screw and Washer (4 Req'd Gas, 2 Req'd Diesel)
4N623333-S100U-Nut (4 Req'd)
519D734A/C Manifold and Tube
619835Condenser to Evaporator Tube
7Refrigerant Identification Tag (Part of 19D734)
819A688Refrigerant Charge Information Tag
ATighten to 14-19 Nm (10-14 Lb-Ft)

 

A/C Compressor

The FS-10 A/C compressor is a 10-cylinder swash-plate type and is installed on the left side of the engine compartment. It is driven by the front end accessory drive belt (8620). Tension adjustment is obtained by means of an automatic tensioner.



 

Spring Lock Coupling

The spring lock coupling found on some fittings in the A/C system is a refrigerant line coupling held together by a garter spring inside a circular cage. When the coupling is connected, the flared end of the female fitting slips behind the garter spring inside the circular cage of the male fitting. The garter spring and circular cage then prevent the flared end of the female fitting from pulling out of the cage. Two O-ring seals are used to seal the two halves of the coupling. These O-ring seals are made of a special material and must be replaced with an O-ring seal of the same material. These O-ring seals can be identified by a green color. These special green O-ring seals are designed for use in R-134a refrigerant systems. Use only the O-ring seals specified in the Ford Master Parts Catalog for the spring lock coupling. The O-ring seals must be replaced each time the spring lock coupling is disconnected and reconnected for servicing or replacement purposes.

A plastic indicator ring is used on spring lock couplings to indicate, during vehicle assembly, that the coupling is connected. Once the coupling is connected, the indicator ring is no longer necessary but remains captive on the refrigerant line, near the spring lock coupling. The indicator ring may also be used for servicing purposes to indicate coupling connection. After the coupling has been cleaned, new green O-rings should be lubricated with clean refrigerant oil and installed. Insert the tabs of the indicator ring into the circular cage opening. Then connect the coupling together by pushing with a slight twisting motion. When the coupling is connected, the indicator ring will pop out of the circular cage indicating connection. Once the spring lock coupling is connected, an A/C tube lock coupling clip (19E746) is placed over the connection to act as a secondary retention holding device.

Spring Lock Coupling




 

A/C Compressor Pressure Relief Valve

An A/C compressor pressure relief valve (19D644) is installed on the A/C manifold and tube to relieve excess high-pressure buildups (3172 kPa or 460 psi and above) and prevent damage to the A/C compressor and other air conditioner components.