Service Manual

20
remedied with a field installed discharge muffler.
Recommend loop by continuous tubing with no more
than 12 inches vertical and 6 inch horizontal loop.
6. An internal “thunking”, “thumping”, “grinding” or
“rattling” noise could indicate compressor internal
failures and may be verified by comparing the
compressor amperage to what the compressor
should be drawing according to a manufacturer’s
performance data.
7. A whistling or squealing noise during operation may
indicate a partial blockage of the refrigerant charge.
8. A whistle on shut down could indicate a partial leak
path as refrigerant is equalizing from high to low side.
On occasion, an in- line discharge check valve has
prevented this sound.
9. If a compressor hums but won’t start it could indicate
either a voltage or amperage issue. Verify adequate
voltage and operational start components if installed.
If it is drawing excessive amperage and voltage
doesn’t appear to be the problem it may be assumed
a locked condition. Ensure refrigerant has had ample
time to equalize and boil out of the compressor before
condemning.
10. When a heat pump switches into and out of defrost, a
”swooshing” noise is expected due to the rapid
pressure change within the system. However
customers sometimes complain that the noise is
excessive, or it is sometimes accompanied by a
”groaning, or howling” noise. When receiving these
complaints, Quiet Shift- 2 (if available) may improve
the noise, but will probably not eliminate it totally.
Check that the defrost thermostat or thermistor is
operating properly. Insulating the defrost sensing
device may also help. If the howling or groaning noise
is intermittent, replacing the reversing valve may or
may not help.
POWER OFF!
OHMMETER
0-10Ω SCALE
5.2Ω
0.6Ω
5.8Ω
DEDUCTION:
(EXAMPLE)
TO DETERMINE INTERNAL CONNECTIONS OF SINGLE-
PHASE MOTORS (C,S,R) EXCEPT SHADED-POLE
?
?
?
1
2
2
3
1
3
12
32
1 3 (GREATEST RESISTANCE)
5.8Ω (OHM)
(SMALLEST RESISTANCE)
0.6Ω
(REMAINING RESISTANCE)
5.2Ω
2
2
3
1
IS COMMON (C)
BY ELIMINATION
IS COMMON,
THEREFORE, IS
START WINDING (S)
RUN WINDING (R)
START WINDING (S)
IS RUN WINDING (R)
A88344
Fig. 12 – Identifying Compressor Terminals
11. Rattling that occurs during a shift into or out of defrost
on a heat pump could indicate a pressure differential
issue. This is usually a brief occurrence (under 60
seconds) and can be remedied by incorporating Quiet
Shift- 2, if available. This is a feature available in
communicating heat pumps that shuts down the
compressor during the defrost shift for approximately
1 minute allowing the pressures to equalize. It is
enabled by either a dip switch setting on the defrost
board, or in the wall control on Communicating
systems. Verify proper system charge as well.
A07124
Fig. 13 – Split Post Grommet part number: 1172271
Note: Long radius elbows recommended
A07123
Fig. 14 – Suction Line Loop
Electrical Failures
The compressor mechanical pump is driven by an electric
motor within its hermetic shell. In electrical failures,
compressor does not run although external electrical and
mechanical systems appear normal. Compressor must be
checked electrically for abnormalities.
Before troubleshooting compressor motor, review this
description of compressor motor terminal identification.