32
SYSTEM OPERATION
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 atmospheric
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 temperature 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 pressures 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 superheated 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 transferred 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 bypass
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
thermostat 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
thermostat 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.