N4H7T: Installation Instructions
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
9
Unloader Test Procedure
The unloader is the compressor internal mechanism, controlled by the
DC solenoid, that modulates between high and low stage. If it is
suspected that the unloader is not working, the following methods may
be used to verify operation.
1. Operate the system and measure compressor amperage. Cycle the
unloader on and off at 30 second plus intervals at the thermostat
(from low to high stage and back to low stage). Wait 5 seconds
after staging to high before taking a reading. The compressor
amperage should go up or down at least 20 percent.
2. If the expected result is not achieved, remove the solenoid plug
from the compressor and with the unit running and the thermostat
calling for high stage, test the voltage output at the plug with a DC
voltmeter. The reading should be 24 volts DC.
3. If the correct DC voltage is at the control circuit molded plug,
measure the compressor unloader coil resistance. The resistance
should be approximately 1640 milliohms. If the coil resistance is
infinite or is grounded, the compressor must be replaced.
Final Checks
IMPORTANT:
Before leaving job, be sure to do the following:
1. Ensure that all wiring is routed away from tubing and sheet metal
edges to prevent rub-through or wire pinching.
2. Ensure that all wiring and tubing is secure in unit before adding
panels and covers. Securely fasten all panels and covers.
3. Tighten service valve stem caps to 1/12-turn past finger tight.
4. Leave Owner’s Manual with owner. Explain system operation and
periodic maintenance requirements outlined in manual.
5. Fill out Dealer Installation Checklist and place in customer file.
Troubleshooting
If the compressor fails to operate with a cooling call, the table below
(Resistance table) can be used to verify if there is any damage to the
compressor windings causing system malfunction.
Major Components
2-Stage Compressor
The 2-stage compressor contains motor windings that provide 2-pole
(3500 RPM) operation.
Compressor Internal Relief
The compressor is protected by an internal pressure relief (IPR) which
relieves discharge gas into compressor shell when differential between
suction and discharge pressures exceeds and 550 - 625 psi. The
compressor is also protected by an internal overload attached to motor
windings.
Compressor Control Contactor
The contactor has a 24 volt coil and is controlled by Y1 input from the
thermostat
Low Pressure Switch
Low pressure switch is provided in line with the Y1 signal to the
contactor for protection.
Care and Maintenance
For continuing high performance and to minimize possible equipment
failure, periodic maintenance must be performed on this equipment.
Frequency of maintenance may vary depending upon geographic areas,
such as coastal applications. See Users Manual for information.
Table 3 – Winding Resistance
Winding
Winding resistance at 70°F +/- 20°F
(21.11°C +/- 11.11°C)
Unit Size
024
036
048
060
Start (S-C)
1.652
1.587
1.299
1.203
Run (R-C)
1.065
0.751
0.477
0.383
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