Air Conditioning System Operation


The A/C system provides the following features:

Cooled or 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 the heater and air conditioning blower case. The forward movement of the vehicle forces 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. A gravity feed through a drain hole removes the moisture from the vehicle. This action dehumidifies the air.

    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 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.

    FREON AND COMPONENT OPERATION

    Most of todays systems used on this vehicle is a non-cycling system. Non-cycling A/C systems use a high pressure switch to protect the A/C system from excessive pressure. 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 refrigerant 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 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. 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 - 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?

    • 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 - Keith

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

    • Guest - krisit

      2002 grand prix a/c blows hot air on driver side and cold air on passenger side. Can any one tell me what needs to be fixed on this ? Please I would appreciate it a lot.

    • Guest - Tom

      In reply to: Guest - krisit

      You have a bad temperature door actuator. Search us for that. You will find several articles.

    • Guest - nathan

      Buick Century 2000 does not blow any air, hot or cold?

    • Guest - Tech

      In reply to: Guest - nathan

      Possible causes are a bad blower motor, blower motor resistor and / or connector, a blown fuse. Check fuses first, then check the resistor. It is located near the blower motor under the passenger side of the dash.

    • Guest - Rhenny

      The problem in the A/C is not blowing enough cold. The freon was newly charged. A mechanic said the problem is the freon used was made in China. He recommends the one made in the USA. Another mechanic said the problem is in the compressor. I had the evaporator cleaned before and the valve was replaced with a new one.

    • Guest - Tech

      In reply to: Guest - Rhenny

      The problem in the A/C is not blowing enough cold, the freon was newly charged. A mechanic said the problem is the freon used was made in China. He recommends the one made in the USA. Another mechanic said the problem is in the compressor. I had the evaporator cleaned before and the valve was replaced with a new one
      <br />What make model and year is this car or truck Rhenny?

    • Guest - Charlene

      My 2005 Equinox cools great while moving, but while idling, gets too warm.

    • Guest - Tech

      In reply to: Guest - Charlene

      My 2005 Equinox cools great while moving, but while idling, gets too warm.
      <br />As with any problem of A/C not blowing cold enough, the first thing is to make sure the freon charge is sufficient. Just putting gauges on and looking at readings may not be enough. If the system is even a 1/2 pound low on freon, the gauges will read fine, but the system will not cool properly. Especially at idle and in very humid weather. If the charge is good, then you need to make sure that the radiator fan is running and the condenser (it is in front of the radiator) is clean. If these all check out, then you may need to do a control head re-calibration.

    • Guest - wilbert

      1999 Chevy Tahoe front air blows cool, rear air blows cold. The a/c filled with freon.

    • Guest - Tech

      In reply to: Guest - wilbert

      This problem can be caused by a faulty temperature door actuator motor. This is what controls the temperature door for the front. It is located under the dash, to the left of the glove opening. Or you could have a bad heater control valve on the heater hose under the hood causing the air to be warmed up a little.