System Operation; Cooling; Heating; Cooling Cycle - Daikin ComfortNet DX16TC Series Service Instructions Manual

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 cool-
er 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 refrig-
erant cycle illustrations on the following pages are for demon-
stration 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 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 bypass
the indoor expansion device. The check valve at the outdoor
coil will be forced closed by the refrigerant flow, thereby utiliz-
ing the outdoor expansion device.

COOLING CYCLE

For communicating room thermostat: When the room thermo-
stat calls for either low stage cool or high stage cool, appro-
priate 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 thermo-
stat calls for either low stage heat or high stage heat, appro-
priate 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.
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