How A/C works

A/C system July 14, 2011

Where does the cold air come from?  Modern A/C systems use refrigerant to absorb heat.  The refrigerant absorbs heat from the interior of a vehicle in a component called the evaporator.  Air is pushed across the evaporator and since the evaporator is colder then the air coming across it the heat is absorbed by the refrigerant, resulting in cold air being blown into the passenger compartment.  This air is really the same air but has the heat removed or absorbed.  The heat that was absorbed is now absorbed in the refrigerant, and with the A/C compressor pumping the refrigerant is moved to the A/C condenser.  The condenser's job is to dissipate the heat.  The compressor has increased our pressure, we have an enormous amount of heat loss across the face of the condenser.  As the refrigerant is pushed across the condenser it sheds the absorbed heat from the passenger compartment.  The refrigerant still under high pressure, and with heat removed the refrigerant is now ready to absorb heat again.  The refrigerant is then pushed thru a small orifice called a "orifice tube" or expansion block which drops the pressure in the A/C system.  Once the pressure is reduced it is pushed thru the evaporator again to absorb heat again from the passenger compartment.  The components:

The A/C compressor:  The A/C compressor the A/c compressor is the hardest working component of the air conditioning system.  The traditional design consists of pistons and valves.  Other styles include vanes and some are a scroll type a/c compressor.  Considerable heat is generated by a compressor, and the cold refrigerant returning to the compressor is vital to its longevity.  If an A/C system is not full to capacity, the compressor is not receiving enough cold refrigerant and oil, and overheating of moving parts and seals is occurring, and a shortened compressor life is inevitable. 

The Condenser: The A/C condenser receives high pressure refrigerant from the A/C compressor, thru a series of small tubes allows heat energy contained in the refrigerant to transfer to the condenser, and on to the air rushing thru the condenser.  The condenser is located in front of the radiator in front of the vehicle in order to allow maximum amount of air flow.   In the A/C condenser the refrigerant is both a gas and a liquid.  As the refrigerant enters the condenser it is very hot, high pressure gas.  As the gas passes thru the condenser, sufficient cooling allows the hot gas to condenser and turn into a liquid by the time it leaves the condenser.  An enormous amount of heat is shed in this process. 

The expansion valve:  The expansion valve has one job, and that's to drop the pressure.  The pressure can be 250-300 psi are common and by the time the refrigerant passes thru the valve they will drop to 20-30 psi.  This drastic pressure drop allows the refrigerant to be very cold and ready to absorb heat. 

The evaporator:  The evaporator receives cold low pressure refrigerant from the expansion valve.  This allows heat absorption.  In the evaporator the hot air from the evaporator there is enough heat in the air to boil the refrigerant.  An enormous amount of heat energy is absorbed this way.  As the refrigerant leaves the evaporator, it is transformed almost completely to a gas. 

The A/C drier:  The A/C drier, as heat load increases or decreases , the refrigerant expands or contracts.  The drier allows this to happen in this space.  Located inside the drier are fabric pouches that contain silicon beads that absorb moisture. 

The rest of the A/C system is made up of hoses, pipes, wiring, switches, modules, motors, fans, doors, actuators, and refrigerant.  All vehicles have most of these additional items.  The A/C systems are getting more and more complex as vehicles are getting more efficent.  If there is any questions or you feel there is more then you want to dive into.  Please feel free to contact us:  Triangle auto service, 4060 N. Elston, Chicago Il. 60618, 773-539-5858.,, or


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