Service Manual

19
A12344
4. Slide out the sensor, slide in replacement and reinstall
the cover
A12345
COMPRESSOR TROUBLESHOOTING
Compressor Failures
Compressor failures are classified in 2 broad failure
categories; mechanical and electrical. Both types are
discussed below.
Mechanical Failures
A compressor is a mechanical pump driven by an electric
motor contained in a welded or hermetic shell. In a
mechanical failure, motor or electrical circuit appears
normal, but compressor does not function normally.
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal
injury or death.
Do not supply power to unit with compressor terminal
box cover removed.
!
WARNING
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal
injury or death.
Exercise extreme caution when reading compressor
currents when high- voltage power is on. Correct any of
the problems described below before installing and
running a replacement compressor.
!
WARNING
Locked Rotor
In this type of failure, compressor motor and all starting
components are normal. When compressor attempts to
start, it draws locked rotor current and cycles off on internal
protection. Locked rotor current is measured by applying a
clamp- on ammeter around common (blk) lead of
compressor. Current drawn when it attempts to start is then
measured. Locked rotor amp (LRA) value is stamped on
compressor nameplate.
If compressor draws locked rotor amps and all other
external sources of problems have been eliminated,
compressor must be replaced. Because compressor is a
sealed unit, it is impossible to determine exact mechanical
failure. However, complete system should be checked for
abnormalities such as incorrect refrigerant charge,
restrictions, insufficient airflow across indoor or outdoor coil,
etc., which could be contributing to the failure.
Runs, Does Not
Pump
In this type of failure, compressor motor runs and turns
compressor, but compressor does not pump refrigerant. A
clamp- on amp meter on common leg shows a very low
current draw, much lower than rated load amp (RLA) value
stamped on compressor nameplate. Because no refrigerant
is being pumped, there is no return gas to cool compressor
motor. It eventually overheats and shuts off on its internal
protection.
Noisy
Compressor
Noise may be caused by a variety of internal and external
factors. Careful attention to the “type” of noise may help
identify the source. The following are some examples of
abnormal conditions that may create objectionable noise:
1. A gurgling sound may indicate a liquid refrigerant
floodback during operation. This could be confirmed if
there is no compressor
superheat. A compressor
superheat of “0” degrees would indicate liquid
refrigerant returning to the compressor. Most common
reasons for floodback are: loss of evaporator blower,
dirty coils, and improper airflow.
2. A rattling noise may indicate loose hardware. Inspect
all unit hardware including the compressor grommets.
3. A straining (hard start) or vibration occurring at start
up but clears quickly after could indicate an off cycle
refrigerant migration issue. Refrigerant migration can
occur when a compressor is off and refrigerant vapor
transfers from other areas of the system, settles into
the compressor as it is attracted to the oil, and then
condenses into the oil. Upon start up, the compressor
draws suction from within itself first and lowers the
boiling point of the refrigerant that is entrained in the
oil. This can cause the liquid refrigerant and oil to boil
into the compression area or liquid refrigerant to wipe
off oil films that are critical for proper lubrication.
Migration is worsened by greater temperature
differentials and/or extra refrigerant in the system.
Prevention of migration can be reduced by various
options but some of the more common remedies is to
verify proper charge and add a crankcase heater
where this situation is suspected.
4. Operational vibration could indicate a charge issue.
Verify charge and ensure proper piping and structural
penetration insulation. Tubing that is too rigid to
building rafters without proper insulation could
transfer noise throughout the structure. On some
occasions a sound dampener or mass weight (FAST
part no. 1185726) placed on the vibrating tubing has
been known to reduce this noise. Utilizing
compressor split post grommets (see Fig. 13) may
also reduce this vibration if piping cannot be
remedied.
5. An operational high pitch frequency or “waa waa”
sound that appears to resonate through the suction
line could indicate a need to add more flex or muffling
in the lines. This has been occasional in scroll
compressor applications and is usually remedied by
adding a field- fabricated suction line loop (see Fig.
14). Reciprocating compressors may have a
noticeable discharge pulsation that could be