Bryant 127A - Manual (Page 6)

6
Check Charge
The 127A units may be charged in high-- or low--stage compressor
operation. 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 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, See Long Line Guideline for
special 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 opera-
tion 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.
Table 3 – Winding Resistance
Winding
Winding resistance at 70_F +/--- 20_F
(21.11_C +/--- 11.11_C)
127A024 127A036 127A048 127A060
Start
(S---C)
2.74 1.98 1.55 0.6
Run
(R---C)
0.8 0.75 0.48 0.49
Troubleshooting 127A units 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. 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 DC signal to 24v AC.
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 run-
ning 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 32 to 60 ohms depending on com-
pressor temperature. If the coil resistance is infinite, much
lower than 32 ohms, or is grounded, the compressor must
be replaced.
127A