Lennox XP19-024 Instruction Manual page 6

INTERNAL SOLENOID (L34)
The internal unloader solenoid controls the two−stage op-
eration of the compressor by shifting a slide ring mecha-
nism to open (low capacity) or close (high capacity), two
by−pass ports in the first compression pocket of the scrolls
in the compressor. The internal solenoid is activated by a
24 volt direct current solenoid coil. The internal wires
from the solenoid in the compressor are routed to a 2 pin
fusite connection on the side of the compressor shell. The
external electrical connection is made to the compressor
with a molded plug assembly. The molded plug receives 24
volt DC power from the LSOM II.
If it is suspected the unloader is not operating properly,
check the following
IMPORTANT
This performance check is ONLY valid on systems
that have clean indoor and outdoor coils, proper air-
flow over coils, and correct system refrigerant
charge. All components in the system must be func-
tioning proper to correctly perform compressor
modulation operational check. (Accurate measure-
ments are critical to this test as indoor system load-
ing and outdoor ambient can affect variations be-
tween low and high capacity readings).
STEP 1 Confirm low to high capacity compressor
operation
Tools required
Refrigeration gauge set
Digital volt/amp meter
Electronic temperature thermometer
On-off toggle switch
TWO−STAGE MODULATION
Bypass Ports
Closed
High Capacity
FIGURE 8
Procedure
1−. Turn main power "OFF" to outdoor unit.
2−. Adjust room thermostat set point above (heating op-
eration on heat pump) or below (cooling operation) the
room temperature 5ºF.
3−. Remove control access panel. Install refrigeration
gauges on unit. Attach the amp meter to the common
(black wire) wire of the compressor harness. Attach
thermometer to discharge line as close as possible to
the compressor.
4−. Turn toggle switch "OFF" and install switch in series
with Y2 wire from room thermostat.
5−. Cycle main power "ON."
6−. Allow pressures and temperatures to stabilize before
taking any measured reading (may take up to 10 min-
utes).
NOTE − Block outdoor coil to maintain a minimum of 375
psig during testing).
7−. Record all of the readings for the Y1 demand on table
1.
8−. Close switch to energize Y2 demand.
9−. Allow pressures and temperatures to stabilize before
taking any measured reading (this may take up to 10
minutes).
10−.Record all of the readings of Y2 demand on table 1.
NOTE − On new installations or installations that have
shut down for an extended period of time, if the com-
pressor does not cycle from low stage to high stage on
the first attempt, it may be necessary to recycle the com-
pressor back down to low stage and back up to high
stage a few times in order to get the bypass seals to
properly seat
Compare Y1 readings with Y2 readings in table 1. Some
readings should be higher, lower or the same. If the
readings follow what table 1 specifies, the compressor is
operating and shifting to high capacity as designed. If the
readings do not follow what table1 specifies, continue to
step 2 to determine if problem is with external solenoid
plug power.
Page 6
Bypass Ports
Open
Low Capacity