Millennium Scroll Compressor - Carrier 38TN Service Manual

Y—Energizes contactor for cooling.
C—Common side of transformer (blk).

MILLENNIUM SCROLL COMPRESSOR

(R134A REFRIGERANT)
The compressor used in this product is specifically designed for
use with R134A 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 tech-
niques. Refrigerants in system present other safety hazards.
Always wear safety glasses and gloves when handling refrig-
erants.
The scroll compressor pumps refrigerant through the system by the
interaction of a stationary and an orbiting scroll. (See Fig. 14.) 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.
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.
2
The open passage is sealed off
as gas is drawn into the spiral.
4
By the time the gas arrives at
the center port, discharge
pressure has been reached.
Fig. 14—Scroll Compressor Refrigerant Flow
The Millennium scroll has a shutdown flapper valve located
between the scroll plates and the discharge head. The discharge
head remains under pressure during shutdown and requires a
factory supplied PTC start thermistor.
The Millennium scroll compressor uses Mobil 68POE, the only oil
recommended for oil recharge. Oil recharge for the Millennium
SCD compressor is 34 fl. oz. and the SRD compressor is 52 fl. oz.
Compressor failures are classified in 2 broad failure categories;
mechanical and electrical. Both types are discussed below.
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3
As the spiral continues to orbit,
the gas is compressed into an
increasingly smaller pocket.
5
Actually, during operation, all
six gas passages are in various
stages of compression at all
times, resulting in nearly con-
tinuous suction and discharge.
A90198
Step 1—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.
To avoid personal injury or death, do not supply power to unit
with compressor terminal box cover removed.
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. Wear safety glasses and gloves when handling
refrigerants.
LOCKED ROTOR — In this type of failure, compressor motor
and all starting components are normal. When compressor at-
tempts to start, it draws locked rotor current and cycles off on the
internal protection. Locked rotor current is measured by applying
a clamp-on ammeter around common (blk) lead of the 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
the refrigerant. A clamp-on ammeter 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 problems such as loosened hardware, broken mounting
springs, etc. System problems such as an overcharged compressor
(especially at start-up) or too much oil in compressor may also
cause excessive noise. Excess oil in compressor is encountered
only after a replacement compressor has been added without
purging oil from previous compressor. As the new compressor
pumps, excess oil in system returns and adds to volume already
present, causing noise.
COMPRESSOR LEAKS
Use safety glasses and gloves when handling refrigerants.
Sometimes a leak is detected at weld seam around girth of
compressor, or at a fitting that joins compressor shell. Many of
these leaks can be repaired and the compressor saved if correct
procedure is followed.
1. Turn off all power to unit.
2. Remove and recover all refrigerant from system so that gage
pressures are 0 psi.
3. Clean area around leak to bare metal.
4. Apply flux and repair joint with silver solder. Do not use low
temperature solder such as 50-50.
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