Lennox SSB*H4 Manual page 8

INTERNAL SOLENOID (L34)
The internal unloader solenoid controls the two−stage op-
eration of the compressor by shifting a slide ring mechanism
to open two by−pass ports in the first compression pocket of
the scrolls in the compressor. The internal solenoid is acti-
vated by a 24 volt direct current solenoid coil. The coil
power requires 20VAC. 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 con-
nection is made to the compressor with a molded plug as-
sembly. This plug contains a full wave rectifier that converts
24 volt AC into 24 volt DC power to power the unloader sole-
noid. Refer to unit diagram for internal circuitry view of plug).
If it is suspect 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 mod-
ulation operational check. (Accurate measurements
are critical to this test as indoor system loading and
outdoor ambient can affect variations between low
and high capacity readings).
STEP 1 Confirm low to high capacity compressor op-
eration
Tools required
Refrigeration gauge set
Digital volt/amp meter
Electronic temperature thermometer
On-off toggle switch
Procedure
1 − Turn main power "OFF" to outdoor unit.
2 − Adjust room thermostat set point above (heating opera-
tion 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 compres-
sor does not cycle from low stage to high stage on the
first attempt, it may be necessary to recycle the compres-
sor 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 read-
ings follow what table 1 specifies, the compressor is oper-
ating and shifting to high capacity as designed. If the
readings do not follow what table 1 specifies, continue to
step 2 to determine if problem is with external solenoid
plug power.
Page 8