Daikin DAR09 - System Operation: Cooling and Heating; Cooling Cycle Overview

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SYSTEM OPERATION
COOLING
The refrigerant used in the system is R-410A. It is a clear, color-
less, non-toxic and non-irritang 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 refrigeraon
cycle possible are: heat always ows 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 o
and condensed at a higher pressure and temperature to be used
again.
The indoor evaporator coil funcons to cool and dehumidify the
air condioned spaces through the evaporave process taking
place within the coil tubes.
NOTE: The pressures and temperatures shown in the refrigerant
cycle illustraons on the following pages are for demonstraon
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 refrig-
erant enters the tubes of the indoor coil, a poron of the liquid
immediately vaporizes. It connues to soak up heat and vaporiz-
es as it proceeds through the coil, cooling the indoor coil down
to about 48°F.
Heat is connually being transferred to the cool ns 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 o by the vapor.
As the vapor passes through the last tubes of the coil, it be-
comes superheated. That is, it absorbs more heat than is neces-
sary 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, rst loses its superheat by heat transferred from
the gas through the tubes and ns of the coil. The refrigerant
now becomes saturated, part liquid, part vapor and then con-
nues to give up heat unl it condenses to a liquid alone. Once
the vapor is fully liqueed, it connues to give up heat which
subcools the liquid, and it is ready to repeat the cycle.
HEATING
The heang poron of the refrigeraon cycle is similar to the
cooling cycle. By energizing the reversing valve solenoid coil, the
ow of the refrigerant is reversed. The indoor coil now becomes
the condenser coil, and the outdoor coil becomes the evapora-
tor coil.
The check valve at the indoor coil will open by the ow of
refrigerant leng the now condensed liquid refrigerant bypass
the indoor expansion device. The check valve at the outdoor coil
will be forced closed by the refrigerant ow, thereby ulizing the
outdoor expansion device.
The restrictor orice used with the CA*F, CHPF and CH**FCB
coils will be forced onto a seat when running in the cooling
cycle, only allowing liquid refrigerant to pass through the orice
opening. In the heang cycle, it will be forced o the seat
allowing liquid to ow around the restrictor. A check valve is not
required in this circuit.
COOLING CYCLE
For legacy room thermostat: When the room thermostat calls
for cool, the contacts of the room thermostat close making
terminals R to Y1 & G (if thermostat calls for low stage cool), or
R to Y1, Y2 & G (if thermostat calls for high stage cool), the low
voltage circuit of the transformer is completed. Current now
ows through the magnec holding coils of the compressor con-
tactor (CC) and fan relay (RFC). If thermostat calls for high stage
cool, the microprocessor on the UC board will also energize the
compressor high stage solenoid to run the compressor at full
capacity.
This draws in the normally open contact CC, starng the com-
pressor and condenser fan motors in either low or high stage
depending on the thermostat’s demand. At the same me,
contacts RFC close, starng the indoor fan motor.
When the thermostat is sased, it opens its contacts, breaking
the low voltage circuit, causing the compressor contactor and
indoor fan relay to open, shung down the system.
If the room thermostat fan selector switch should be set on the
“on” posion, then the indoor blower would run connuously
rather than cycling with the compressor.
DZ11S, DZ13S, DZ14S, DZ16S, DS16 and DZ18 models energize
the reversing valve thorough the “O” circuit in the room ther-
mostat. Therefore, the reversing valve remains energized as long
as the thermostat subbase is in the cooling posion. The only
excepon to this is during defrost.
For heat pumps, during cooling cycle the reversing valve is ener-
gized as the room thermostat closes “O” terminal to R and the
microprocessor on the UC board responds to such a condion by
energizing the solenoid coil on the reversing valve.