How does Car AC work?

Air conditioning (AC) in cars used to be a luxury during the 1960s, but it has become a necessity in modern day cars. A vehicle's air conditioner doesn't actually cool the air. It just removes the heat and moisture out of the air present within the vehicle. The car AC works on two cycles: refrigeration and evaporative cooling.

Car AC works on the same principle as the home/office ACs. It has five main components:

1. Compressor
2. Condenser
3. Receiver dryer
4. Expansion valve
5. Evaporator coil

The freon/refrigerant is used in AC system. The refrigerant is circulated through the entire system in closed circuit.

Compressor:

As the name suggests, compressor is used to compress the refrigerant to high pressure and temperature. In home ACs, compressor is run through electric motor. In cars, the compressor is driven by a belt connected to the engine crankshaft. A magnetic clutch is used to engage/disengage the compressor to the belt. Once compressed, the gaseous refrigerant is pushed out through discharge valve to the condenser.  

  

Condenser:

Condenser acts as a radiator to remove the heat from the refrigerant. Condenser sits in front of the car, just behind the front grille and in front of the car radiator. Ambient air passes through the condenser and removes the heat from the refrigerant. The high pressure gaseous refrigerant is converted into high pressure liquefied refrigerant.

Receiver Dryer:

The purpose of dryer is to remove the impurities and moisture from the liquefied refrigerant. It can also be used as a temporary storage tank for liquefied refrigerant.

Expansion Valve:

Expansion valve is used to control the amount of refrigerant entering the evaporator. It has a small hole which lets the valve to spray the refrigerant. As the high pressure refrigerant passes into the expansion valve, both pressure and temperature drop and it is sprayed into the evaporator in a misty form.

Evaporator:

Evaporator acts like a radiator. The low pressure, low temperature refrigerant in gaseous form passes through the coils inside the evaporator. A blower fan pulls the heat out from inside the vehicle cabin and blows the warm air over the evaporator. Since the temperature inside the evaporator is lower, it absorbs the heat from the blower and leaves behind cooler air. This cooled air is circulated into the car cabin. The refrigerant which is hot now and in gaseous form is circulated back to the compressor and the cycle keeps repeating.

Blower

Refrigerant:

Freon-R12 was used commonly but due to its damaging effects on the ozone layer, manufacturers have replaced it with R-134a.