There are three major types of air conditioning systems in modern cars, all of which have a very similar concept and design and as such can be explained as one. Your air conditioning system consists of a compressor, condenser, evaporator, orifice tube and a receiver-drier. In some systems you may have a thermal expansion valve instead of an orifice tube, and either a receiver drier or accumulator, as each these are effectively variations of the same component, you will have one of each.
Diagram of an Air conditioning system layout
The compressor is a belt driven pump which is run by the engine, it compresses and transfers refrigerant gas (such as Freon in older cars – see this article for more details) The air conditioning system works strangely like a heart with half of it under high pressure and half under low pressure, (discharge and suction). The intake side draws the gas from the evaporator (in some cars via an accumulator), it is then compressed and sent to the condenser.
The condenser looks just like a car radiator and is where the heat dissipates, it is usually found just in front of the radiator. Hot compressed gases enter the condenser and are cooled and leave as a high-pressure liquid.
The Evaporator is primarily to remove heat from inside a vehicle as well as dehumidifying the air. Warm air enters the evaporator coil and condenses on its surface, on humid days you can see this dripping from the bottom of your car, this is normal so don’t worry if you notice this! The evaporator operates best at 32 degrees F (zero Celsius), meaning when refrigerants enter as liquid and meets the warm air it begins to boil (as these gases have a very low boiling point) at this point the refrigerant absorbs a lot of heat from the car and it is carried away, cooling down the car.
Pressure regulating devices are used to control the pressure and subsequent temperature of the refrigerants; either the Orifice tube or the thermal expansion valve does this job. A TXV (thermal expansion valve) is a valve sensitive to pressure and temperature, they are efficient but can suffer from clogging and corrosion. Whereas an orifice tube (commonly found in GM and Ford vehicles) is a much cheaper option and is about three inches long, and found in the inlet tube of the evaporator, but they are easily clogged and replacing them can be hard as it means opening up the system and removing many parts, so TXV’s are becoming more and more popular.
A receiver-drier is found on in systems, which contain a thermal expansion valve and is part of the high-pressure section. It effectively makes sure that the refrigerant is separated into liquid and gas form and other uses include removing moisture and filtering out dirt. An accumulator also splits gas and liquid, in this case providing gas to the compressor, as introducing liquid to it can be very dangerous.
Now we know how it works then.. how do you diagnose some of the more common problems which you may encounter?
TROUBLESHOOTING COMMON PROBLEMS:
1. Start off with the obvious, check your dashboard and make sure you have air conditioning actually switched on, rather than just recalculating the air. The A/C switch actually physically turns on the compressor and allows air to be circulated: you’d be surprised how often this mistake is made!
2. Check you fans, you should be able to hear them blowing smoothly not whistling or whining, if it is your fan motors could be damaged and need to be replaced, and if it doesn’t work at all you may want to try checking the fuse first. This is fairly easy and tool is usually included as well as a tool to do the job, and the fuses are clearly labeled, if it still doesn’t work, see a mechanic.
3. If your fans work and there is still no cold air then you most likely have a problem with one of the aforementioned components, you can try following the supply line, it is a black tube going from the engine area through the dash, if it has any holes or splits then the cool air will be escaping! But you will still need to see a mechanic I’m afraid
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