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GA7T: Installation Instructions
Compressor Operation
The basic scroll design has been modified with the addition of an
internal unloading mechanism that opens a by-pass port in the first
compression pocket, effectively reducing the displacement of the scroll.
The opening and closing of the by-pass port is controlled by an internal
electrically operated solenoid. The modulated scroll uses a single step of
unloading to go from full capacity to approximately 67% capacity. A
single speed, high efficiency motor continues to run while the scroll
modulates between the two capacity steps. Modulation is achieved by
venting a portion of the gas in the first suction pocket back to the low
side of the compressor, thereby reducing the effective displacement of
the compressor. Full capacity is achieved by blocking these vents, thus
increasing the displacement to 100%.
A DC solenoid in the compressor controlled by a rectified 24 volt AC
signal in the external solenoid plug moves the slider ring that covers and
uncovers these vents. The vent covers are arranged in such a manner that
the compressor operates at approximately 67% capacity when the
solenoid is not energized and 100% capacity when the solenoid is
energized. The loading and unloading of the two step scroll is done "on
the fly" without shutting off the motor between steps.
NOTE:
67% compressor capacity translates to approximately 75%
cooling capacity at the indoor coil.
Check Charge
NOTE: CHARGE IN HIGH STAGE ONLY
Factory charge amount and desired subcooling are shown on unit rating
plate. Charging method is shown on information plate inside unit. To
properly check or adjust charge, conditions must be favorable for
subcooling charging. Favorable conditions exist when the outdoor
temperature is between 70°F and 100°F (21.11°C and 37.78°C), and the
indoor temperature is between 70°F and 80°F (21.11°C and 26.67°C).
Follow the procedure below:
Unit is factory charged for 15ft (4.57 m) of lineset. Adjust charge by
adding or removing 0.6 oz/ft of 3/8 liquid line above or below 15ft (4.57
m) respectively.
For standard refrigerant line lengths (80 ft/24.38 m or less), allow system
to operate in high-stage cooling mode at least 15 minutes. If conditions
are favorable, check system charge by subcooling method. If any
adjustment is necessary, adjust charge slowly and allow system to
operate for 15 minutes to stabilize before declaring a properly charged
system.
If the indoor temperature is above 80°F (26.67°C), and the outdoor
temperature is in the favorable range, adjust system charge by weight
based on line length and allow the indoor temperature to drop to 80°F
(26.67°C) before attempting to check system charge by subcooling
method as described above.
If the indoor temperature is below 70°F (21.11°C), or the outdoor
temperature is not in the favorable range, adjust charge for line set length
above or below 15ft (4.57 m) only. Charge level should then be
appropriate for the system to achieve rated capacity. The charge level
could then be checked at another time when the both indoor and outdoor
temperatures are in a more favorable range.
NOTE: If line length is beyond 80 ft (24.38 m) or greater than 20 ft
(6.10 m) vertical separation,
charging requirements.
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.
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
See Long Line Guideline for special
TROUBLESHOOTING
If the compressor fails to operate with a cooling call,
to verify if there is any damage to the compressor windings causing
system malfunction.
Table 3 – Winding Resistance
Winding resistance at 70°F +/- 20°F
Winding
24
Start (S-C)
1.652
Run (R-C)
1.065
Troubleshooting for proper switching between low-
and high-stages
Check the suction pressures at the service valves. Suction pressure
should be reduced by 3-10% when switching from low to high stage.
NOTE: The liquid pressures are very similar between low- and high-
stage operation, so liquid pressure should not be used for
troubleshooting.
Compressor current should increase 20 to 45% when switching from low
to high stage. The compressor solenoid when energized in high stage,
should measure 24vac at the leads inside control box.
When the compressor is operating in low stage, the 24v DC compressor
solenoid coil is de-energized. When the compressor is operating in high
stage, the 24v DC solenoid coil is energized.
The solenoid plug harness that is connected to the compressor has an
internal rectifier that converts the 24v AC signal to 24v DC.
DO NOT INSTALL A PLUG WITHOUT AN INTERNAL
RECTIFIER.
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 10 seconds
after staging to high before taking a reading. The compressor
amperage should go up or down at least 20 percent.
2. If step one does not give the expected results, 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.
7
Table 3
can be used
(21.11°C +/- 11.11°C)
Unit Size
36
48
1.587
1.299
1.203
0.751
0.477
0.383
60
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