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PRODUCT DESIGN
FIGURE A
A scroll is an involute spiral which, when matched with a mating
scroll form as shown, generates a series of crescent shaped gas
pockets between the two members.
During compression, one scroll remains stationary (fixed scroll)
while the other form (orbiting scroll) is allowed to orbit (but not
rotate) around the first form.
As this motion occurs, the pockets between the two forms are
slowly pushed to the center of the two scrolls while simultane
-
ously being reduced in volume. When the pocket reaches the
center of the scroll form, the gas, which is now at a high pres
-
sure, is discharged out of a port located at the center.
During compression, several pockets are being compressed
simultaneously, resulting in a very smooth process. Both the
suction process (outer portion of the scroll members) and the
discharge process (inner portion) are continuous.
Some design characteristics of the Compliant Scroll compressor
are:
• Compliant Scroll compressors are more tolerant of liquid
refrigerant.
NOTE: Even though the compressor section of a Scroll
compressor is more tolerant of liquid refrigerant, continued
floodback or flooded start conditions may wash oil from the
bearing surfaces causing premature bearing failure.
• "Ultratech" Series scroll compressors use "POE" or polyo
-
lester oil which is NOT compatible with mineral oil based
lubricants like 3GS. "POE" oil must be used if additional oil is
required.
• Compliant scroll compressors perform “quiet” shutdowns
that allow the compressor to restart immediately without
the need for a time delay. This compressor will restart even
if the system has not equalized.
NOTE:
Operating pressures and amp draws may differ from
standard reciprocating compressors. This information can be
found in the unit’s Technical Information Manual.
CAPACITY CONTROL - LEGACY MODELS
During the compression process, there are several pockets with
-
in 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
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 uncov
-
ers 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:
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.
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