Service Instructions

PRODUCT DESIGN
76
CAPACITY CONTROL - LEGACY MODELS
During the compression process, there are several pockets within
the scroll that are compressing gas. Modulation is achieved by
venting a portion of the gas in the first suction pocket back to the
low side of the compressor thereby reducing the effective dis-
placement 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 fly” without shutting off the motor between
steps. See Figure B below. The unloaded mode default was chosen
for two reasons:
Molded Plug w/
Rectifier
24 Va
c
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 heat-
ing if desired.
UNLOADER SOLENOID
A nominal 24-volt direct current coil activates 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 connection 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 rectifier 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-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 con-
densed 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.