Air Conditioning System Operation

The A/C system provides the following features:

Cooled and dehumidified air for the comfort of the occupants. Power ventilation. Windshield defrosting. Side window defrosting.

During most operating conditions outside air enters the vehicle in the following manners:

The blower motor pulls in outside air through an intake in the col near the wiper arms through the heater and air conditioning blower case. The forward movement of the vehicle and the low pressure it creates in this area helps force in outside air.

Air flows along the following path within the evaporator module:

Through the evaporator core

  • Through the heater core

    The flow of air through the heater core is determined by the positions of the right and left temperature valves.

    Into the passenger compartment

    If the ambient temperature is above 7°C (45°F), the refrigeration system will chill the evaporator to almost freezing. This action permits operation of the air conditioning or defroster functions.

    As the air passes through the evaporator the air temperature drops. Air moisture condenses on the evaporator core fins and collects. A gravity feed through a drain hole in the case removes the moisture from the vehicle. This action dehumidifies the air. You notice this as water leaking under the passenger side of the car.

    From the evaporator some or all of the air may pass through the heater core. If the system is in the heating mode, the engine coolant in the heater core warms the air.

    If the user selects the A/C RECIRC mode, most of the air that enters the blower motor is from the passenger compartment. The air from the passenger compartment is usually cooler than the outside air. The other modes use only outside air.



    Most of today's air conditioning systems used on vehicles is a non-cycling system. Non-cycling A/C systems use a high pressure switch to protect the A/C system from excessive pressure. Pressure is constantly controlled by a variable wave plate inside the compressor. The high pressure switch will OPEN the electrical signal to the compressor clutch, if the refrigerant pressure becomes excessive. After the high and the low sides of the A/C system pressure equalize, the high pressure switch will CLOSE. This completes the electrical circuit to the compressor clutch. The A/C system is also mechanically protected with the use of a high pressure relief valve. If the high pressure switch were to fail or if the refrigerant system becomes restricted and refrigerant pressure continues to rise, the high pressure relief will pop open and release freon from the system.

    The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure on the vapor refrigerant. Compressing the refrigerant also adds heat. The refrigerant is discharged from the compressor through the discharge hose, and forced through the condenser and then through the balance of the A/C system.

    Compressed refrigerant enters the condenser at a high-temperature, high-pressure vapor state. As the refrigerant flows through the condenser, the heat is transferred to the ambient air passing through the condenser. Cooling causes the refrigerant to condense and change from a vapor to a liquid state.

    The condenser is located in front of the radiator for maximum heat transfer. The condenser is made of aluminum tubing and aluminum cooling fins, which allows rapid heat transfer for the refrigerant. The semi-cooled liquid refrigerant exits the condenser and flows through the liquid line to the orifice tube.

    The orifice tube is located in the liquid line between the condenser and the evaporator. The orifice tube is the dividing point for the high and the low pressure sides of the A/C system. As the refrigerant passes through the orifice tube, the pressure on the refrigerant is lowered, causing the refrigerant to vaporize at the orifice tube. The orifice tube also measures the amount of liquid refrigerant that can flow into the evaporator.

    Refrigerant exiting the orifice tube flows into the evaporator core in a low-pressure liquid state. Ambient air is drawn through the HVAC case module and passes through the evaporator core. Warm and moist air will cause the liquid refrigerant to boil inside the evaporator core. The boiling refrigerant absorbs heat from the ambient air and draws moisture onto the evaporator and collects. The refrigerant exits the evaporator through the suction line and flows back to the compressor in a vapor state, completing the A/C cycle of heat removal. At the compressor the refrigerant is compressed again and the cycle of heat removal is repeated.

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  • Guest - Keith

    my 2002 Chevy Impala climate control is out if its out will a clutch work

  • Guest - Barbara

    Jeep grand Cherokee a/c won't operate properly-- fan doesn't blow until 55 mph. Sometimes comes on when engine first started; then it abruptly cuts off. Help!

  • Guest - bill

    In reply to: Guest - Barbara

    Jeep grand Cherokee a/c won't operate properly-- fan doesn't blow until 55 mph. Sometimes comes on when engine first started; then it abruptly cuts off. Help!
    <br />
    Jeep grand Cherokee a/c won't operate properly-- fan doesn't blow until 55 mph. Sometimes comes on when engine first started; then it abruptly cuts off. Help!
    <br />The fan coming on at 55 mph is probably just air flow from outside since you are going so fast. Your fan is not working. Check for a bad connection at the fan motor and the relay.

  • Guest - Anthony

    A/C only blows cold air for a few minutes in the daytime then at night blows cold air till I turn the car off . Been through 3 new compressors , 1 new accumulator , and had orfice filter changed . Also checked for system leaks 3 times . Please help .

  • Guest - Billy

    In reply to: Guest - Anthony

    With all this guessing at pars it would be hard to tell what is wrong. We need to know if the compressor is kicking off or if the temp door in the dash is moving. What are the pressures?