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B − Two−Stage Scroll Compressor (B1)
FIGURE 9
TWO−STAGE MODULATED SCROLL
solenoid actuator coil
slider ring
The scroll compressor design is simple, efficient and re-
quires few moving parts. A cutaway diagram of the scroll
compressor is shown in figure 1.The scrolls are located in
the top of the compressor can and the motor is located just
below. The oil level is immediately below the motor.
The scroll is a simple compression concept centered
around the unique spiral shape of the scroll and its inherent
properties. Figure 10 shows the basic scroll form. Two iden-
tical scrolls are mated together forming concentric spiral
shapes (figure 11). One scroll remains stationary, while the
other is allowed to orbit" (figure 12). Note that the orbiting
scroll does not rotate or turn but merely orbits" the station-
ary scroll.
FIGURE 10
SCROLL FORM
The counterclockwise orbiting scroll draws gas into the outer
crescent shaped gas pocket created by the two scrolls (fig-
ure 4 − 1). The centrifugal action of the orbiting scroll seals off
the flanks of the scrolls (figure 4 − 2). As the orbiting motion
continues, the gas is forced toward the center of the scroll
and the gas pocket becomes compressed (figure 4 −3).
When the compressed gas reaches the center, it is dis-
charged vertically into a chamber and discharge port in the
top of the compressor (figure9). The discharge pressure
forcing down on the top scroll helps seal off the upper and
lower edges (tips) of the scrolls (figure 11). During a single
orbit, several pockets of gas are compressed simultaneous-
ly providing smooth continuous compression.
FIGURE 11
STATIONARY
SCROLL
ORBITING SCROLL
DISCHARGE
SUCTION
CROSS−SECTION OF SCROLLS
TIPS SEALED BY
DISCHARGE PRESSURE
DISCHARGE
PRESSURE
The scroll compressor is tolerant to the effects of liquid re-
turn. If liquid enters the scrolls, the orbiting scroll is allowed
to separate from the stationary scroll. The liquid is worked
toward the center of the scroll and is discharged.
Due to its efficiency, the scroll compressor is capable of
drawing a much deeper vacuum than reciprocating com-
pressors. Deep vacuum operation can cause internal fusite
arcing resulting in damaged internal parts and will result in
compressor failure. This type of damage can be detected
and will result in denial of warranty claims. The scroll com-
pressor can be used to pump down refrigerant as long as
the pressure is not reduced below 7 psig.
NOTE During operation, the head of a scroll compres-
sor may be hot since it is in constant contact with dis-
charge gas.
The scroll compressors in all SPB*H4 model units are de-
signed for use with HFC−410A refrigerant and operation at
high pressures. Compressors are shipped from the factory
with 3MA (32MMMA) P.O.E. oil. See electrical section in
this manual for compressor specifications.
TWO−STAGE OPERATION
The two−stage scroll compressor operates like any stan-
dard scroll compressor with the exception the two−stage
compressor modulates between first stage (low capacity
approximately 67%) and second stage (high capacity).
Modulation occurs when gas is bypassed through bypass
ports (figure 13 bypass ports open) in the first suction pock-
et. This bypassing of gas allows the compressor to operate
on first stage (low capacity) if thermostat demand allows.
Indoor thermostat setting will determine first or second
stage operation. The compressor will operate on first−stage
until demand is satisfied or the indoor temperature reaches
the thermostat set point calling for second−stage.
Second−stage (high capacity) is achieved by blocking the
bypass ports (figure 13 bypass ports closed) with a slider
ring. The slider ring begins in the open position and is con-
trolled by a
24VDC
internal solenoid. On a Y2 call the inter-
nal solenoid closes the slider ring, blocking the bypass
ports and bringing the compressor to high capacity. Two−
stage modulation can occur during a single thermostat de-
mand as the motor runs continuously while the compressor
modulates from first−stage to second− stage.
