The air conditioning system in your car has four basic parts, a compressor that is driven by the cars engine, two heat exchangers, the condenser and the evaporator. Then there is the refrigerant that flows through the system.
Here is how the system works. The Freon is compressed, then flows through the condenser where it will be cooled into a liquid then passed through the drier / receiver to remove any moisture. When the Freon goes through the expansion valve the high pressure liquid turns into a vapor and comes out cold as it goes through the evaporator.
Common problems with automotive air conditioners:
There is no air coming out the vents:
1) Defective air conditioner relay
2) Loose or broken connection in wiring
3) Blown A/C fuse
4) Low pressure switch is bad
5) Fan resistor pack if bad
The air conditioner blows warm air out:
1) The actuator for the electronic blend door is not working
2) The air conditioner has a leak in the system
3) Compressor clutch not engaging
Water collects on the interior floor when the air conditioner is on:
The drain hose for the evaporator has come off or disconnected
The evaporator drain hose is blocked. Remove and clear blockage
Air conditioner has a bad smell when on:
The drain hose to the evaporator is restricted or blocked allowing condensation
to build up around the drainage tray and evaporator. Clear the drain hose where it exits the car.