A/C Refrigerant System Operation

THE REFRIGERANT CYCLE
During stabilized conditions (air conditioning system shutdown), the refrigerant is in a vaporized state and pressures are equal throughout the system. When the A/C compressor is in operation it increases pressure on the refrigerant vapor raising its temperature. The high-pressure and high-temperature vapor is then released into the top of the A/C condenser core.

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. The now liquid refrigerant, still at high pressure, exits from the bottom of the A/C condenser core and enters the inlet side of the A/C evaporator core orifice.

The A/C evaporator core orifice is the restriction in the refrigerant system that creates the high pressure buildup upstream of the A/C condenser core and separates the high and low pressure sides of the A/C system. As the liquid refrigerant leaves this restriction, its pressure and boiling point are reduced.

The liquid refrigerant is now at its lowest pressure and temperature. As it passes through the A/C evaporator core, its absorbs heat from the passenger compartment airflow passing over the plate/fin sections of the A/C evaporator core. This addition of heat causes the refrigerant to boil (change to gas). The now cooler passenger compartment air can no longer support the same humidity level of the warmer air and this excess moisture condenses on the exterior of the evaporator coils and fins and drains outside the vehicle.

The suction accumulator/drier is designed to remove moisture from the refrigerant and to prevent any liquid refrigerant that may not have been vaporized in the evaporator core from reaching the A/C compressor. The A/C compressor is designed to pump refrigerant vapor only, as liquid refrigerant will not compress and can damage the A/C compressor.

The refrigerant cycle is now repeated with the A/C compressor again increasing the pressure and temperature of the refrigerant.

The A/C cycling switch interrupts compressor operation before the external temperature of the A/C evaporator core gets low enough to cause the condensed water vapor (excess humidity) to turn to ice. It does this by monitoring low side line pressure. It is known that a refrigerant pressure of approximately 210 kPa (30 psi) will yield an operating temperature of 0°C (32°F). The A/C cycling switch controls system operation in an effort to maintain this temperature.

The A/C high side line pressure is also monitored so that A/C compressor operation can be interrupted if system pressure becomes too high.

The A/C compressor relief valve will open and vent refrigerant to relieve unusually high system pressure.

SYSTEM AIR FLOW






MAX A/C
When MAX A/C is selected:
- The air inlet duct door is at full vacuum, closing off outside air and admitting only recirculated air.
- The panel vent air flow door and the defrost/floor air flow door are at full vacuum, directing airflow to the A/C registers.
- Temperature control is usually set for maximum cold but may be heated if selected.
- Air will be picked up at the recirc opening by the blower motor. With the temperature control set for maximum cold, airflow across the A/C evaporator core will be diverted past the heater core and then directed into the passenger compartment through the instrument panel A/C registers.
- The A/C compressor will be enabled when MAX A/C is selected.
- The blower motor is on.







A/C
When A/C is selected:
- The air inlet duct door is set at no vacuum, blocking the recirc passage and admitting outside air.
- All other door positions are the same as MAX A/C.
- Temperature setting can be changed manually.
- The A/C compressor will be enabled when A/C is selected.
- The blower motor is on.







PANEL
When VENT is selected:
- The air inlet duct door, with no vacuum being applied, will block recirculated air and admit outside air. From there, air flows through the system to the instrument panel A/C registers.
- The panel vent air flow door is at full vacuum to block airflow to the heater assembly floor ducts.
- The defrost/floor air flow door is at full vacuum, closing off airflow to the windshield defroster hose nozzles.
- The temperature setting can be changed manually to heat the air but air cannot be cooled below outside temperature.
- The A/C compressor will be disabled when VENT is selected.
- The blower motor is on.







OFF
When OFF is selected:
- The A/C inlet duct door is at full vacuum, closing off outside air and admitting only recirc air.
- The panel vent air flow door is at no vacuum and the defrost/floor air flow is at full vacuum, closing off the passages to the A/C registers.
- The blower motor and the A/C compressor are off.








PANEL/FLOOR
When PANEL/FLOOR is selected:
- The air inlet duct door is set at no vacuum, blocking the recirc passage and admitting outside air.
- The heater panel vent air flow door is in the partial vacuum position, allowing airflow to both the A/C registers and the heater assembly floor ducts.
- The defrost/floor air flow door is at full vacuum, closing off airflow to the windshield defroster hose nozzle and directing airflow to the heater outlet floor duct.
- The A/C compressor will be enabled when PANEL/FLOOR is selected.
- The blower motor is on,







FLOOR
When FLOOR is selected:
- The air inlet duct door is in the no vacuum position, blocking recirc air and admitting outside air.
- The defrost/floor air flow door is in the vacuum position, closing off airflow to the windshield defroster hose nozzles.
- The temperature control can be positioned to mix air flowing through and around the heater core to achieve the selected temperature level.
- The panel vent air flow door is in the no vacuum position, blocking air circulation to the panel A/C registers.
- The A/C compressor will be disabled when FLOOR is selected.
- The blower motor is on.







FLOOR/DEFROST
When FLOOR/DEFROST is selected:
- The air inlet duct door is in the no vacuum position blocking recirc air and admitting outside air.
- The defrost/floor air flow door is in the partial vacuum position, allowing airflow to both the windshield defroster hose nozzle and the heater assembly floor ducts.
- The panel vent air flow door is in the no vacuum position.
- The A/C compressor will be enabled when FLOOR/DEFROST is selected to dehumidify the air and reduce windshield fogging.
- The blower motor is on.







DEFROST
When DEFROST is selected:
- The air inlet duct door is in the no vacuum position, admitting outside air.
- Both the panel vent air flow door and the defrost/floor air flow door are in the no vacuum position so that most of the incoming air is directed to the windshield defroster hose nozzle. There is also airflow to the side window demister and hose.
- The temperature control knob setting will determine the amount of air that is directed through the heater core and the amount that bypasses the heater core.
- The A/C compressor will be enabled when DEFROST is selected to dehumidify the air and reduce windshield fogging.
- The blower motor is on.