No Air Conditioning
Definitely the most likely reason your air conditioning is not working is the refrigerant level is low or there is none at all. Certainly there may be other reasons your air conditioning system is not working but for this article I will stick with a low or no refrigerant condition.
The refrigerant in your vehicle’s air conditioning system travels in a closed loop from inside to outside. Along the way it experiences two state changes; liquid to gas and then gas to liquid. The liquid to gas state change takes place in the vehicle and provides the cooling effect.
The amount of refrigerant in the system determines the effectiveness. A low refrigerant level will have limited cooling capacity. The air blowing on you from the vents will be not much different than the air blowing on you if you open the windows. Too much refrigerant will have the same effect but the only way to get too much refrigerant is a botched refilling procedure.
From the time your vehicle was originally filled with refrigerant on the assembly line it began to slowly leak out. Where your home refrigerator or home air conditioning system has all metal piping your vehicle has some rubber type hoses in certain sections. Hose materials are more permeable to refrigerant than metal piping.
Every automotive air conditioning system has a compressor. This pump of sorts is driven by the engine and it moves the refrigerant around the loop. The front of the compressor has a rotating shaft with a seal to keep the refrigerant in. This seal is not a perfect seal and therefore a frequent leakage element (especially as the system ages).
There are two other major components that hold refrigerant but are often the culprits for leaks.
The condenser and the evaporator. They are both usually made of aluminum. The evaporator hides in the bowels of your dashboard area and it usually leaks from corrosion. Sometimes it corrodes from the inside out and other times outside in. Leaves and junk dropping from trees get in through the air vents at the bottom of your windshield and makes a nice acidic slurry that might gradually eat a hole into the evaporator.
The condenser is in front of and looks like the radiator. As you can imagine it is blasted with all kinds of stuff. Rocks, sand, salt and curbs come to mind.
When the technician finds a low or no refrigerant condition some sleuthing is required to find the leak or leaks. A big leak may be sleuthed just by a simple visual inspection or by filling the system up with nitrogen and listening for the hiss of a large leak.
Small leaks are much more of a challenge. There are a variety of leak detection devices designed for these situations. Some of these are electronic devices that essentially sniff for leaking refrigerant. Another common practice is the addition of a fluorescent dye to the refrigerant. The customer will be told to use the vehicle for a while and then return for an inspection with UV light.
It is always possible that there is no significant leak in the system. It just might be the simple loss of refrigerant with age through hoses, seals and connections. In this case the system can simply be refilled and put back into service.