SYSTEM OPERATION
15
COOLING
The refrigerant used in the system is R-22. It is a clear,
colorless, non-toxic, non-irritating, and non-explosive liquid.
The chemical formula is CHCLF
2
. The boiling point, at
atmospheric pressure is -41.4°F.
A few of the important principles that make the refrigeration
cycle possible are: heat always flows from a warmer to a
cooler body, under lower pressure a refrigerant will absorb
heat and vaporize at a low temperature, the vapors may be
drawn off and condensed at a higher pressure and tempera-
ture to be used again.
The indoor evaporator coil functions to cool and dehumidify
the air conditioned spaces through the evaporative process
taking place within the coil tubes.
NOTE:
The pressures and temperatures shown in the
refrigerant cycle illustrations on the following pages are for
demonstration purposes only. Actual temperatures and pres-
sures are to be obtained from the "Expanded Performance
Chart."
Liquid refrigerant at condensing pressure and temperatures,
(270 psig and 122°F), leaves the outdoor condensing coil
through the drier and is metered into the indoor coil through
the metering device. As the cool, low pressure, saturated
refrigerant enters the tubes of the indoor coil, a portion of the
liquid immediately vaporizes. It continues to soak up heat and
vaporizes as it proceeds through the coil, cooling the indoor
coil down to about 48°F.
Heat is continually being transferred to the cool fins and tubes
of the indoor evaporator coil by the warm system air. This
warming process causes the refrigerant to boil. The heat
removed from the air is carried off by the vapor.
As the vapor passes through the last tubes of the coil, it
becomes superheated, that is, it absorbs more heat than is
necessary to vaporize it. This is assurance that only dry gas
will reach the compressor. Liquid reaching the compressor
can weaken or break compressor valves.
The compressor increases the pressure of the gas, thus
adding more heat, and discharges hot, high pressure super-
heated gas into the outdoor condenser coil.
In the condenser coil, the hot refrigerant gas, being warmer
than the outdoor air, first loses its superheat by heat trans-
ferred from the gas through the tubes and fins of the coil. The
refrigerant now becomes saturated, part liquid, part vapor and
then continues to give up heat until it condenses to a liquid
alone. Once the vapor is fully liquefied, it continues to give up
heat which subcools the liquid, and it is ready to repeat the
cycle.
HEATING
The heating portion of the refrigeration cycle is similar to the
cooling cycle. By energizing the reversing valve solenoid coil,
the flow of the refrigerant is reversed. The indoor coil now
becomes the condenser coil, and the outdoor coil becomes
the evaporator coil.
The check valve at the indoor coil will open by the flow of
refrigerant letting the now condensed liquid refrigerant by-
pass the indoor expansion device. The check valve at the
outdoor coil will be forced closed by the refrigerant flow,
thereby utilizing the outdoor expansion device.
The restrictor orifice used with the CA*F, CHPF coils and the
AR*F air handler will be forced onto a seat when running in
the cooling cycle, only allowing liquid refrigerant to pass
through the orifice opening. In the heating cycle it will be
forced off the seat allowing liquid to flow around the restrictor.
A check valve is not required in this circuit.
COOLING CYCLE
When the contacts of the room thermostat close making
terminals R to Y & G, the low voltage circuit of the transformer
is completed. Current now flows through the magnetic hold-
ing coils of the compressor contactor (CC) and fan relay
(RFC).
This draws in the normally open contact CC, starting the
compressor and condenser fan motors. At the same time
contacts RFC close starting the indoor fan motor.
When the thermostat is satisfied, it opens its contacts,
breaking the low voltage circuit, causing the compressor
contactor and indoor fan relay to open, shutting down the
system.
If the room thermostat fan selector switch should be set on
the "on" position, then the indoor blower would run continuous
rather than cycling with the compressor.
Heat pumps energize the reversing valve thorough the "O"
circuit in the room thermostat. Therefore the reversing valve
remains energized as long as the thermostat subbase is in
the cooling position. The only exception to this is during
defrost.
DEFROST CYCLE
The defrosting of the outdoor coil is jointly controlled by the
defrost timing board, defrost (30/60) control, and compressor
run time.
HEATING CYCLE
The reversing valve on the heat pump models is energized in
the cooling cycle through the "O" terminal on the room
thermostat.
These models have a 24 volt reversing valve coil. When the
thermostat selector switch is set in the cooling position, the
"O" terminal on the thermostat is energized all the time.
Care must be taken when selecting a room thermostat. Refer
to the installation instructions shipped with the product for
approved thermostats.
