SYSTEM OPERATION
24
COOLING
The refrigerant used in the system is R-410A. It is a clear,
colorless, non-toxic and non-irritating liquid. R-410A is a
50:50 blend of R-32 and R-125. The boiling point at atmo-
spheric pressure is
-62.9°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.
COOLING CYCLE
For communicating room thermostat: When the room ther-
mostat calls for either low stage cool or high stage cool,
appropriate commands are sent via the data 1 and data 2 lines
to the outdoor unit's UC control. The UC control energizes the
on-board compressor relay and the on-board outdoor fan
relay. The compressor high stage solenoid is energized if it
is a high stage call.
The UC control sends a fan command to the indoor unit (air
handler or furnace). The indoor unit operates the indoor
blower at the appropriate airflow level. The system operates
at the cooling level demanded by the thermostat.
When the thermostat is satisfied, appropriate commands are
sent to the UC control. The compressor relay and outdoor
fan relay is de-energized. The compressor high stage
solenoid is de-energized if it was energized. The UC control
sends an appropriate command to the indoor unit to de-
energize the indoor blower motor.
If room thermostat fan status is set to be “on”, then indoor
blower would run continuously rather than cycling with the
compressor.
For heat pumps, the reversing valve is energized during the
cooling cycle. The call for cooling from the communicating
thermostat indicates to the control that the reversing valve is
to be energized during cooling operation.
HEATING CYCLE
For communicating room thermostat: When the room ther-
mostat calls for either low stage heat or high stage heat,
appropriate commands are sent via the data 1 and data 2 lines
to the outdoor unit's UC control. The UC control energizes the
on-board compressor relay and the on-board outdoor fan
relay. The compressor high stage solenoid is energized if it
is a high stage call. The UC control sends a fan command
to the indoor unit (air handler or furnace). The indoor unit
operates the indoor blower at the appropriate airflow level.
The system operates at the cooling level demanded by the
thermostat.
