Would you like to know how your vehicle's air conditioner works? The system looks complicated, but it's really quite simple. Once you know how it delivers cold air you will be better informed when problems occur and how to fix them.
What does it do?
Not only does the air conditioner cool the passenger compartment, it operates when the defroster is on as well. This seems strange but, many manufactures run the AC system in the defroster mode. The reason for this is to remove moisture while keeping the windshield dry from humidity. Sometimes you will notice plain water leaking from under the passengers side of the car about where the passenger foot well would be, this is normal and is the result of moisture build up on the evaporator core which you will learn about further down in this guide. When the air condition system is on it will reduce the car's MPG slightly, it will also cause the engine to run warmer, this is why the radiator cooling fans operate while passing air over the AC condenser.
How Does It Work?
When you give the command to have the air conditioner come on, the blower motor will start to run at the desired speed while energizing the compressor of the system. The HVAC system blend door actuators will then adjust the vent air flow to allow the air through the evaporator. This is where the coolness is generated and then pushed through the dashboard vents.
Here is a short description of the air conditioner system components and what the do:
Compressor: Acts as the pump which circulates the refrigerant.
Condenser: Located in front of the engine radiator and cools the refrigerant into a liquid state.
Receiver Dryer: Removes moisture from inside the system to prevent rust and corrosion.
Expansion Valve/Orifice Tube: Releases high pressure refrigerant gas into the evaporator. (Each part does basically the same thing, though an expansion valve can vary the amount of refrigerant passed through it to help control temperature.)
Evaporator: Accepts low pressure refrigerant which is cool and allows the blower motor to pass air through it.
High Side Service Port: This is where a pressure gauge set is attached and monitored.
Low Side Service Port: Where the refrigerant is added while the system is running and the pressure monitored.
High Pressure Hose: This hose and fittings transfer refrigerant from the compressor to the condenser, and then to the receiver dryer, then onto the expansion valve/orifice tube.
Low Pressure Hose: Transfers the expelled refrigerant from the evaporator to the compressor.
High and Low Side Pressure Sensors: Used to monitor the system for safety and performance controls.
REFRIGERANT
Commonly known as "Freon" which was a popular brand name, is part fluid, part gas, which is held under pressure inside the AC system. When the system is not running the refrigerant remains a gas under low pressure, about 70 psi. When the system is activated (switched on) the compressor will bring the high side to about 235 PSI where it is pushed through an expansion valve or orifice tube, causing the low side pressure to drop to about 45 PSI inside the evaporator.
The entire action is basically a high pressure liquid, then released into a low pressure gas. If you take a can of hair spray and then release the product (hair stiffener), along with the propellant, the spray-can will get the cold. The exact same chemical reaction used by the air conditioner, the only exception is the gas is recovered inside the evaporator and then recycled into the system. The refrigerant is transferred from one component to another by using hoses or tubes.
PS: This guide knowledge base comes from the 2CarPros team and Ken Lavacot.