COMPRESSOR - The A/C compressor pumps the refrigerant through the system. It's operated by an engine belt, just like the alternator and power steering pump. The only difference is that the A/C compressor has a clutch that engages and disengages the compressor as needed. When you turn off the system, the A/C compressor clutch disengages, and no longer causes a drag on the engine.

REFRIGERANT - A little physics if you don't mind: There's no such thing as "cold" - there's only a lack of heat. The A/C system doesn't pump "cold" into the car, it extracts heat from the inside of the car and pumps it out into the atmosphere. It does this by the use of the refrigerant chemical. In older cars, the chemical was R12 (freon). Since R12 contains chlorine and flourine, it damages the ozone layer and its production was banned. R12 has been replaced by R134a, which is more ozone-friendly since it doesn't contain chlorine or flourine. R12 is still available for purchase, but it's getting really expensive. R134a can be retrofitted into the older systems if all of the old oil and refrigerant is removed first.

Let's follow the refrigerant's path, once it leaves the compressor:

CONDENSOR - This is the thin radiator in front of your engine's radiator. At this point, the refrigerant is extremely hot and under high pressure--80 to 300 psi, depending on the environmental conditions. The condenser acts as a radiator, removing heat from the refrigerant, and in the process, changing it from a gas to a liquid. Now that the refrigerant is cooler and liquid again, it's sent on to the expansion valve.

EXPANSION VALVE and EVAPORATOR CORE - These act as a heat absorption unit, removing heat from the inside of the car. The expansion valve is designed to meter the flow of refrigerant based on the heat load it senses coming from the evaporator. It also changes the refrigerant from a liquid to a gas. A little more physics: when a liquid changes to a gas, it absorbs heat - lots of it.

The evaporator core absorbs heat from the inside of the car, sort of like a radiator in reverse. It does this when the blower fans blow warm air over the evaporator core. Once the system is in operation, the heat absorbed by the evaporator core is transferred to the refrigerant at the moment of evaporation. Dehumidification also takes place during air conditioning, since cold air can't hold as much moisture as warm air. All this gives you cool dry air inside your car, and leaves the big water puddle that you see when you park your car after the A/C has been operating.

RECEIVER/DRYER - This component acts as a filter, trapping small particles and removing any residual moisture from the system. Any moisture in the system will freeze up at the expansion valve and will clog the system, so it has to be removed. Then, it's back to the compressor, and the cycle starts over.

Remember, anyone can perform mechanical work on an A/C system without a license, but no one is allowed to vent any refrigerant into the atmosphere. A license is required to purchase the refrigerant and charge the system. If you need to replace a component in your A/C system, have the system professionally purged before you open it up to the atmosphere. SAFETY WARNING: opening up a charged system can cause SERIOUS injury.

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