Page 6
FIGURE 2
SCROLL FORM
FIGURE 3
STATIONARY
SCROLL
ORBITING SCROLL
DISCHARGE
SUCTION
CROSS−SECTION OF SCROLLS
TIPS SEALED BY
DISCHARGE PRESSURE
DISCHARGE
PRESSURE
The counterclockwise orbiting scroll draws gas into the outer
crescent shaped gas pocket created by the two scrolls (figure
4 − 1). The centrifugal action of the orbiting scroll seals off the
flanks of the scrolls (figure 4 − 2). As the orbiting motion con-
tinues, 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 discharged vertical-
ly into a chamber and discharge port in the top of the com-
pressor (figure1). The discharge pressure forcing down on
the top scroll helps seal off the upper and lower edges (tips) of
the scrolls (figure 3 ). During a single orbit, several pockets of
gas are compressed simultaneously providing smooth con-
tinuous compression.
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. If the com-
pressor is replaced, conventional Lennox cleanup practices
must be used.
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 compressor
may be hot since it is in constant contact with discharge
gas.
The scroll compressors in all HSXA19 model units are de-
signed for use with R410A 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 standard
scroll compressor with the exception the two−stage com-
pressor modulates between first stage (low capacity
approximately 67%) and second stage (high capacity).
Modulation occurs when gas is bypassed through bypass
ports (figure 5 bypass ports open) in the first suction pocket.
This bypassing of gas allows the compressor to operate on
first stage (low capacity) if thermostat demand allows. In-
door 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 5 bypass ports closed) with a slider ring.
The slider ring begins in the open position and is controlled
by a
24VDC
internal solenoid. On a Y2 call the internal sole-
noid closes the slider ring, blocking the bypass ports and
bringing the compressor to high capacity. Two−stage modu-
lation can occur during a single thermostat demand as the
motor runs continuously while the compressor modulates
from first−stage to second− stage.
NOTE − During operation, the head of a scroll compressor
may be hot since it is in constant contact with discharge
gas.
