A car AC compressor circulates refrigerant that absorbs heat from the cabin through the evaporator and releases it outside through the condenser.
Main parts
- Compressor.
- Condenser.
- Expansion valve.
- Evaporator.
- Refrigerant.
The cycle
The compressor pressurizes the refrigerant gas. The condenser cools it into a liquid. The valve drops the pressure. The evaporator absorbs heat from cabin air as the liquid turns to gas.
Refrigerant
Newer cars use R1234yf. Older ones use R134a.
Common problems
Low refrigerant, leaks, a failed compressor or a clogged cabin filter.
Closed loop
The air conditioning system moves heat from the inside of the car to the outside using refrigerant in a closed loop. It has four main stages: compression, condensation, expansion and evaporation.
Components
- Compressor: driven by the engine belt, it compresses low pressure refrigerant gas into high pressure, hot gas.
- Condenser: in front of the radiator, it releases heat and turns the gas into liquid.
- Receiver drier or accumulator: filters moisture and debris.
- Expansion valve or orifice tube: lowers pressure and temperature of the refrigerant.
- Evaporator: in the dashboard, where cold refrigerant absorbs heat from the cabin air as a fan blows air across it.
Dehumidifying
As the evaporator cools the air, moisture condenses and drips under the car. A puddle of clear water under the car on a hot day is normal.
Refrigerant types
Older cars (before 1994) used R-12, a CFC banned under the Montreal Protocol. Most cars from the mid-1990s to the mid-2010s use R-134a, and newer vehicles use R-1234yf, which has a much lower global warming potential.
Common problems
- Low refrigerant due to leaks.
- Failed compressor or clutch.
- Clogged condenser or cabin air filter.
- Electrical faults such as blown fuses or relays.
- Blocked drain tube causing wet carpets.
- Musty smell from mold on the evaporator.
Fuel use
Using the A/C can reduce fuel economy by about 4% to over 20%, depending on conditions, according to the Department of Energy.
Servicing
Refrigerant handling in the US requires EPA Section 609 certification. Do not vent refrigerant to the air. Repairs can cost from 150 dollars for a recharge to over 1,000 for a compressor.
Parts and refrigerants
A car air conditioning system is a closed loop that moves refrigerant through the compressor, condenser, receiver drier or accumulator, expansion valve or orifice tube, and evaporator. The compressor, driven by the engine belt, pressurizes the refrigerant, which releases heat at the condenser, then expands and cools at the evaporator inside the dashboard, where a fan blows air across it. The evaporator also removes humidity. Cars made after about 1994 used R-134a, and most new cars since the mid 2010s use R-1234yf, which has a far lower global warming potential, under EPA regulations.
Fuel use and servicing
The Department of Energy says air conditioning can reduce the fuel economy of a conventional vehicle by more than 25 percent in very hot conditions. Symptoms of trouble include weak cooling, warm air, odd noises from the compressor and a musty smell from mold in the evaporator. A recharge service commonly costs about 100 to 300 USD, and a new compressor can cost 500 to 1,200 USD or more. Leaks need repair, because adding refrigerant only temporarily fixes the problem. Technicians who service systems need EPA Section 609 certification. Run the AC for a few minutes every month, even in winter, to keep seals lubricated.
Based on data from the US Department of Energy and the EPA
