Page 68
XP21
Checklists
TWO STAGE COMPRESSOR CHECKOUT
Use this check-out procedure to verify part- and full-load
capacity operation of two-stage modulation compressor.
IMPORTANT
This performance check is ONLY valid on systems that
have clean indoor and outdoor coils, proper airflow over
coils, and correct system refrigerant charge. All
components in the system must be functioning proper to
correctly perform compressor modulation 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).
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 5ºF above (heating
operation) or 5ºF below (cooling operation) the room
temperature.
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. Install switch in series with Y2
wire from room thermostat (see note ** in the Field Op-
erational Checklist on page 68).
5. Cycle main power ON.
6. Allow pressures and temperatures to stabilize before
taking any measured reading (may take up to 10 min-
utes).
7. Record all of the readings for the Y1 demand.
8. Close switch to energize Y2 demand. Verify power is
going to compressor solenoid (see note ** in the Field
Operational Checklist on page 68).
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 with the Y1 and Y2 demand.
11. If temperatures and pressures change in the direction
noted in chart, the compressor is properly modulating
from low to high capacity. (If no amperage, pressures
or temperature readings change when this test is per-
formed, the compressor is not switching between low
and high capacity and replacement is necessary).
12. After testing is complete, return unit to original set up.
XP21 Field Operational Checklist
Unit Readings
Cooling*** Heating***
Y1
First
Stage
Expected results
during Y2 demand
(Toggle switch On)
Y2
Second
Stage
Y1
First Stage
Expected results
during Y2 demand
(Toggle switch On)
Y2 Second
Stage
Compressor
Voltage Same Same
Amperage Higher Higher
Condenser Fan motor
Amperage Same or Higher Same or Higher
Temperature
Ambient Same Same
Outdoor Coil Discharge Air Higher Lower
Compressor Discharge Line Higher Higher
Indoor Return Air Same Same
Indoor Coil Discharge Air Lower Higher
Pressures
Suction (Vapor) Lower Down
Liquid Higher Higher
Note − Heat pump may have a low ambient control or Control that locks in second−stage below its set point. It may be necessary to remove a wire
from the control when performing this check out.
** On the XP21 units, the System Operation Monitor controls the second−stage solenoid coil in compressor.
*** Cooling Mode Operation − Block outdoor coil to maintain a minimum of 375 psig during testing.
Heating Mode Operation − Block indoor coil to maintain a minimum of 375 psig during testing.
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