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COPELAND SCROLL COMPRESSOR
Scroll Gas Flow
Compression in the scroll is
created by the interaction of
an orbiting spiral and a
stationary spiral. Gas enters
an outer opening as one of the
spirals orbits.
The open passage is sealed off
as gas is drawn into the spiral.
By the time the gas arrives at
the center port, discharge
pressure has been reached.
Actually, during operation, all
six gas passages are in various
stages of compression at all
times, resulting in nearly con-
tinuous suction and discharge.
As the spiral continues to orbit,
the gas is compressed into an
increasingly smaller pocket.
1
23
54
A90198
Fig. 11 – Scroll Compressor Refrigerant Flow
The compressors used in these products are specifically designed to
operate with designated refrigerant and cannot be interchanged.
The compressor is an electrical (as well as mechanical) device.
Exercise extreme caution when working near compressors. Power
should be shut off, if possible, for most troubleshooting techniques.
Refrigerants present additional safety hazards.
PERSONAL INJURY HAZARD
Failure to follow this caution may result in personal injury.
Wear safety glasses, protective clothing, and gloves when
handling refrigerant.
CAUTION
!
The scroll compressor pumps refrigerant through the system by the
interaction of a stationary and an orbiting scroll. (See Fig. 11.) The
scroll compressor has no dynamic suction or discharge valves, and
it is more tolerant of stresses caused by debris, liquid slugging, and
flooded starts. The compressor is equipped with an internal
pressure relief port. The pressure relief port is a safety device,
designed to protect against extreme high pressure. The relief port
has an operating range between 550 to 625 psi differential pressure
for Puronr and 350 to 450 psi differential pressure for R--22.
Scrolls have a variety of shut down solutions, depending on model,
to prevent backward rotation and eliminate the need for cycle
protection.
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, DoesNot
Pump
In this type of failure, compressor motor runs and turns
compressor, but compressor does not pump refrigerant. A
clamp--on ampmeter 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.