Two−Stage Operation - Lennox XC16?024 Unit Information

TWO−STAGE OPERATION
NOTE − During operation, the head of a scroll compressor
may be hot since it is in constant contact with discharge
gas.
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
SUCTION
POCKET
1
SUCTION
3
HOW A SCROLL WORKS
SUCTION
STATIONARY SCROLL
HIGH
PRESSURE
GAS
TWO STAGE MODULATION
Bypass Ports
Closed
High Capacity
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.
MOVEMENT OF ORBIT
SUCTION
ORBITING
SCROLL
2
FLANKS
SEALED BY
CENTRIFUGAL
FORCE
4
FIGURE 4
FIGURE 5
Page 6
INTERMEDIATE
PRESSURE
GAS
CRESCENT
SHAPED GAS
POCKET
SUCTION
DISCHARGE
POCKET
Bypass Ports
Open
67% Capacity