Condensing Unit & Heat Pump R410A Service Manual

79
Product Design
During the compression process, there are several pockets
within the scroll that are compressing gas. Modulaon is
achieved by venng a poron of the gas in the rst sucon
pocket back to the low side of the compressor thereby
reducing the eecve displacement of the compressor.
See Figure A. Full capacity is achieved by blocking these
vents, increasing the displacement to 100%. A solenoid in
the compressor, controlled by an external 24-volt ac signal,
moves the slider ring that covers and uncovers these vents.
The vent covers are arranged in such a manner that the
compressor operates somewhere around 67% capacity when
the solenoid is not energized and 100% capacity when the
solenoid is energized. The loading and unloading of the two
step scroll is done “on the y” without shung o the mo-
tor between steps. See Figure B below. The unloaded mode
default was chosen for two reasons:
Molded Plug w/
Rectifier
24 Vac
Line
Line
Run Capacitor
C
R
S
Internal Unloader
Coil
FIGURE B
1. It is expected that the majority of run hours will be in the low
capacity, unloaded mode.
2. It allows a simple two-stage thermostat to control capacity
through the second stage in both cooling and possibly heang if
desired.
UNLOADER SOLENOID
A nominal 24-volt direct current coil acvates the internal
unloader solenoid. The input control circuit voltage must be 18
to 28 volt ac. The coil power requirement is 20 VA. The external
electrical connecon is made with a molded plug assembly. This
plug is connected to the Comfort Alert™ or CoreSense™ Module
(dependent upon which module you are using) which contains a
full wave recer to supply direct current to the unloader coil.
COOLING
The refrigerant used in the system is R-410A. It is a clear,
colorless, 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
refrigerant enters the tubes of the indoor coil, a poron of the
liquid immediately vaporizes. It connues to soak up heat and
vaporizes 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
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, 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