How Your A/C Works
Air conditioning includes both the cooling
and heating of air. It also cleans the air and controls the
An air conditioner is able to cool a building because it
removes heat from the indoor air and transfers it outdoors.
A chemical refrigerant in the system absorbs the unwanted
heat and pumps it through a system of piping to the outside
coil. The fan, located in the outside unit, blows outside
air over the hot coil, transferring heat from the refrigerant
to the outdoor air.
Most air conditioning systems have five mechanical components:
- a compressor
- an expansion valve or metering device
- an evaporator coil and blower
- a chemical refrigerant
Most central air conditioning units operate by means of a
split system. That is, they consist of a "hot" side,
or the condensing unit—including the condensing coil, the
compressor and the fan—which is situated outside your home,
and a "cold" side that is located inside your home.
The cold side consists of an expansion valve and a cold coil,
and it is usually part of your furnace or some type of air
handler. The furnace blows air through an evaporator coil,
which cools the air. Then this cool air is routed throughout
your home by means of a series of air ducts. A window unit
operates on the same principal, the only difference being
that both the hot side and the cold side are located within
the same housing unit.
The compressor (which is controlled by the thermostat) is
the "heart" of the system. The compressor acts as
the pump, causing the refrigerant to flow through the system.
Its job is to draw in a low-pressure, low-temperature, refrigerant
in a gaseous state and by compressing this gas, raise the
pressure and temperature of the refrigerant. This high-pressure,
high-temperature gas then flows to the condenser coil.
The condenser coil is a series of piping with a fan that
draws outside air across the coil. As the refrigerant passes
through the condenser coil and the cooler outside air passes
across the coil, the air absorbs heat from the refrigerant
which causes the refrigerant to condense from a gas to a liquid
state. The high-pressure, high-temperature liquid then reaches
the expansion valve.
The expansion valve is the "brain" of the system.
By sensing the temperature of the evaporator, or cooling coil,
it allows liquid to pass through a very small orifice, which
causes the refrigerant to expand to a low-pressure, low-temperature
gas. This "cold" refrigerant flows to the evaporator.
The evaporator coil is a series of piping connected to a
furnace or air handler that blows indoor air across it, causing
the coil to absorb heat from the air. The cooled air is then
delivered to the house through ducting. The refrigerant then
flows back to the compressor where the cycle starts over again.
Tips for Reducing
the Energy Cost of Your Central A/C