Air Conditioning Basics

Depending on where you live, air conditioning may be an absolute requirement. Unfortunately, air conditioning is not a simple project to add to your ride. There are many components and the components are not small. It is a major task to install air conditioning, The first step is to understand the operation of the air conditioning system.

Evaporation and Condesation

Air conditioners work on the principles of evaporation and condensation. When a liquid turns to a gas, this is called evaporation. It has the unique property of absorbing heat from the surrounding area. By absorbing heat, it cools the surrounding area. Early air conditioners, consisted of a damp towel, that was wrapped inside a tube and hung outside the window. Air would blow through the tube, evaporating the water. The conversion from liquid to the gas state would cool the air inside the vehicle. The drawback is that they are only effect in climates with low humidity.

Early air conditioner called a Car Cooler made by Thermador

Modern vehicles uses special refrigerants that evaporate and condense at a low temperature. The refrigerant is compressed to a liquid state by a compressor then allowed to expand in the evaporator which looks like a small radiator.

Here's a block diagram of a typical air conditioning system

When the liquid expands, it turns into a gas and absorbs heat. Passenger compartment air is blown across the evaporator and loses heat. This cooled air is blown into the passenger compartment. The refrigerant in the gas stage is compressed back to the liquid state to start the cycle all over again. It is a closed system with no loss of refrigerant during the process.

The next step is to understand the components of the air conditioning system and where they are located in the vehicle.

Typical location of air conditioner components

The air conditioning system is made up of the following components:

  • Compressor - It's job is to compress the refrigerant from a gas stage to a liquid stage in preparation for evaporation. Compressors are driven by the fan belt and are mounted next to the engine. The usually have an electric clutch to engage them when the air conditioning is turned on. Otherwise they free wheel. Often, your engine computer will detect that the air conditioning is on and increase the idle speed of your engine to compensate for the extra load on the engine.

  • Fan - This is your radiator fan which you should already have installed. It can be an electric or mechanical fan. It's job in an air conditioning system is to cool down the compressed air conditioning refrigerant. When the refrigerant is compressed from a gas back to a liquid, heat is created and this heat is cooled by air flow.

  • Condenser - The condensor's job is to cool the compressed refrigerant. Compressing gas to a liquid takes a lot of energy which creates heat. Since the purpose of an air conditioning system is to cool things down, we want our refrigerant to be as cool as possible before it expands.

  • Drier - This removes any moisture (not a liquid), gas and filters dirt from the system.

  • Expansion Valve - The compressed refrigerant is at a high pressure, the expansion valve releases the pressure and lets the refrigerant evaporate to start the cooling cycle.

  • Evaporator - This is the reverse of the condensator, the refrigerant is evaporating in these coils absorbing heat from the surrounding area.

  • Blower Fan - The blower fan blows air across the evaporator coils and the air is routed into the passenger compartment. It is the same blower fan that is used for the heater.

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Copyright February 2012 Eugene Blanchard