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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 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
3.
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 3.
NOTE On new installations or installations that have shut
down for an extended period of time, if the compressor
does not cycle from low stage to high stage on the first at-
tempt, it may be necessary to recycle the compressor 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 3. Some
readings should be higher, lower or the same. If the read-
ings follow what table 3 specifies, the compressor is operat-
ing and shifting to high capacity as designed. If the readings
do not follow what table 3 specifies, continue to step 2 to de-
termine if problem is with external solenoid plug power.
TABLE 3
Unit Readings
Compressor Operation
Y1 −
1st-Stage
Expected Results
Y2 −
2nd-Stage
Compressor
Voltage
Same
Amperage
Higher
Condenser Fan motor
Amperage
Same or Higher
Temperature
Ambient
Same
Outdoor Coil Discharge Air
Higher in Cooling
Lower in Heating
Compressor Discharge Line
Higher
Indoor Return Air
Same
Indoor Coil Discharge Air
Lower in Cooling
Higher in Heating
Pressures
Suction (Vapor)
Lower
Liquid
Higher
