Air Conditioner

Article explains how an automotive air conditioner works.

Air conditioning facilitates the removal of heat from inside the passenger compartment of a vehicle by conduction and convection principles. This is performed by pressurizing refrigerant (134a) with a compressor and then releasing the refrigerant inside the evaporator. A frigid evaporator absorbs heat from air passing through it, cold air is then forced out through the vents via the blower motor. Some automobiles are equipped with an automatic climate control system to regulate the temperature inside the car automatically. The climate control module is a computer which monitors and adjusts the temperature set by the driver. The temperature is controlled by a combination of cold air from the air conditioner, and warm air from the heater to achieve the desired temperature. The blower motor speed is controlled by a solid state speed controller. This controller electrically controls the speed of the blower motor and replaces the conventional blower motor resistor system. The climate control system provides cooling, heating and is known as the HVAC (heating, ventilation, air conditioning) system which can be filtered using an air cabin filter.

Climate Control Panel

When having problems with this system some models provide a stored trouble code which can be accessed. To check if your vehicle has this capability check the owner's manual or consult a repair manual.

The system begins at the compressor which is driven by the engine through a serpentine belt. Once the refrigerant is compressed it travels though the high pressure side hose and through the condenser located in front of the radiator where its cooled back into liquid (still under high pressure). After this cooling effect is complete the refrigerant travels to the expansion valve or orifice tube (systems use one or the other depending on manufacturer) which is located on or near the evaporator. At this point the high pressure refrigerant (liquid) is released which causes the cooling action inside the evaporator were the blower fan can push air through it and then throughout the ventilation system.

At this point the refrigerant is in a low pressure gas form and returns to the compressor were it is re-compressed and sent into the system again. Every air conditioner system is a closed system that continuously re-circulates the same refrigerant. Depending on manufacturer the air conditioner relies on a filter to keep contaminates out of the system which could cause damage to the compressor or other components. These filters can be placed at either the high side before or after the condenser which as known as a receiver dryer or on the low side before the evaporator which is known as an accumulator.

Air Conditioner System Configuation
Air Conditioner System


The air conditioning compressor is the refrigerant pump of the air conditioning system. The compressor compresses refrigerant inside the system and circulates it to the condenser and then to the evaporator. The air conditioning compressor is driven by a serpentine belt that is powered by the engine and can be engaged and disengaged by an electromagnetic coil on the front of the compressor. This control signal is provided by the climate control module or switch on the temperature control panel.

Air Conditioner Compressor
Air Conditioner Compressor

To maintain the efficiency of the air conditioner the compressor belt should be checked regularly, if worn it should be replaced. The system's hoses should be checked for deterioration, bubbles, cracks and hardening or oily residue, all could be signs of leakage. The correct refrigerant charge should always be maintained, low system refrigerant charge is a common cause of a weak AC system. Odors can developed in the air conditioning system when a fungus has grown on the evaporator core. Aerosol disinfectants can be used to remedy this condition. While the air conditioner system is running on the full high setting with recirculation feature activated, spray a disinfectant (Lysol, Ozium) into the inlet of the ac system (under the dash on the passenger's side), be aware whatever you spray will come out of the upper vents, so you may not want your face in front of any vents when doing this procedure. Odors can be prevented from returning by repeating this procedure periodically throughout the summer months.

Basic Maintenance

  • Automotive charging kits are available at any auto parts store and it is recommended to buy can with fluorescent refrigerant dye which can help to point out the location of any refrigerant leaks. The kit will have instructions to add the refrigerant safely. Protective eyewear should be used when handling pressurized refrigerant cans.
  • Sometimes bugs, leaves and dust particles can get stuck in the condenser fins. Foreign objects and dirt can be cleaned with the help of a garden hose or compressed air forced through the radiator and condenser backwards until clean.
(Note: The air conditioning system is always under pressure, until the system is discharged completely, no repairs or disassembly should be performed. Eye protection should always be worn when repairing or servicing the air conditioning system.)


Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2014-12-30)