Lesson 3 How Does Air Conditioning Work? Part 2

Evaporator

From the compressor, high-pressure gas is sent to the condenser, where the heat is dissipated and condensed to liquid. The high-pressure liquid flows on to the expansion valve, where it is metered and its pressure is reduced. At the evaporator, the liquid absorbs heat from the air and evaporates to gas. The cycle is then repeated, starting at the compressor.

The evaporator works the opposite of the condenser, here refrigerant liquid is converted to gas, absorbing heat from the air in the compartment.

When the liquid refrigerant reaches the evaporator its pressure has been reduced, dissipating its heat content and making it much cooler than the fan air flowing around it. This causes the refrigerant to absorb heat from the warm air and reach its low boiling point rapidly. The refrigerant then vaporizes, absorbing the maximum amount of heat.

This heat is then carried by the refrigerant from the evaporator as a low-pressure gas through a hose or line to the low side of the compressor, where the whole refrigeration cycle is repeated.

The evaporator removes heat from the area that is to be cooled. A blower becomes a necessary part of the evaporator in the air conditioning system. The blower fans must not only draw heat-laden air into the evaporator, but must also force this air over the evaporator fins and coils where it surrenders its heat to the refrigerant and then forces the cooled air out of the evaporator into the space being cooled.

This continues over and over and over until the room reaches the temperature you want the room cooled to. The thermostat senses that the temperature has reached the right setting and turns off the air conditioner. As the room warms up, the thermostat turns the air conditioner back on until the room reaches the temperature.

Compressor

The purpose of the compressor is to circulate the refrigerant in the system under pressure, this concentrates the heat it contains.

At the compressor, the low pressure gas is changed to high pressure gas. This pressure buildup can only be accomplished by having a restriction in the high pressure side of the system. This is a small valve located in the expansion valve.

The compressor has reed valves to control the entrance and exit of refrigerant gas during the pumping operation. These must be firmly seated. An improperly seated intake reed valve can result in gas leaking back into the low side during the compression stroke, raising the low side pressure and impairing the cooling effect. A badly seated discharge reed valve can allow condensing or head pressure to drop as it leaks past the valve, lowering the efficiency of the compressor.

Two service valves are located near the compressor as an aid in servicing the system. One services the high side, it is quickly identified by the smaller discharge hose routed to the condenser. One is used for the low side, the low side comes from the evaporator, and is larger than the discharge hose.

The compressor is normally belt-driven from the engine crankshaft. Most manufacturers use a magnetic-type clutch which provides a means of stopping the pumping of the compressor when refrigeration is not desired.