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Air Conditioning

A compressor pumps a substance called freon through a coil which has a fan blowing out door air across it

(condensing unit). This cools the hot compressed gas and condenses it to a liquid. Then it leaves the condenser coil and is

pumped up to the evaporator coil. At this point there is a small orifice in which the high pressure liquid is pumped

through. After passing through this orifice the liquid rapidly expands thus evaporating (changing states).

When this happens inside the evaporator coil which has a fan blowing indoor air across it. The Freon

absorbs heat from the coil which it absorbs from the air. The Freon leaves the evaporator coil in the form

of vapor (gas with slight drops of liquid).  Then it enters the compressor in the condensing unit once again being compressed 

and pumped back into the condenser coil. This heat that the condenser blows out is the heat that the Freon gives

up when changing states again.

Heat Pump

A heat pump works in the same way as standard Air-conditioning with the exception of a device called a reversing valve.

This device reverses the flow of Freon to and from the two coils (condenser and evaporator coils). Thus the evaporator coil

becomes the condenser coil and the condenser coil becomes the evaporator. The Freon gives up the heat collected from

the outdoors to the indoor air. Doing this in cold damp conditions outdoors can cause the out door section to 

frost and even ice up on the coil. There is a device in the heat pump called a defrost circuit or defrost timer.

This device temporally reverses the Freon again while in the heat mode, back to A/C mode and stops the outdoor fan.

This melts the frost and/or the ice on the coil. When the system comes out of the defrost cycle one may hear a swooshing

sound with a cloud of steam being ejected from the fan section of the outdoor unit.

This is normal operation for a heat pump in the winter.

 Scott Briggs Air-Conditioning, Heating, & Mechanical Services, LLC  ©2003

e-mail scott@scottbriggs.us