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144
Compressor Discharge Check Valve — A disk-type check
valve in the discharge of the compressor prevents high pressure
discharge gas from flowing rapidly back through the compres-
sor at shutdown. This same check valve prevents a high to low
side bypass in multiple compressor circuits.
COMPRESSOR FUNCTIONAL CHECK
A functional compressor test with the suction service valve
closed to check how low the compressor will pull suction pres-
sure is not a good indication of how well a compressor is per-
forming. Such a test may damage a scroll compressor. The
following diagnostic procedure should be used to evaluate
whether a Copeland scroll compressor is working properly.
1. Proper voltage to the unit should be verified.
2. The normal checks of motor winding continuity and short
to ground should be made to determine if the inherent
overload motor protector has opened or if an internal mo-
tor short or ground fault has developed. If the protector
has opened, the compressor must be allowed to cool suffi-
ciently to allow it to reset.
3. Proper indoor and outdoor blower/fan operation should
be verified.
4. With service gages connected to suction and discharge
pressure fittings, turn on the compressor. If suction pres-
sure falls below normal levels, the system is either low on
charge or there is a flow blockage in the system.
5. If suction pressure does not drop and discharge pressure
does not rise to normal levels, reverse any two of the
compressor power leads and reapply power to make sure
compressor was not wired to run in reverse direction. If
pressures still do not move to normal values, the com-
pressor may be faulty. Reconnect the compressor leads as
originally configured.
6. To test if the compressor is pumping properly, the com-
pressor current draw must be compared to published
compressor performance curves using the operating pres-
sures and voltage of the system. If the measured average
current deviates more than ±15% from published values,
a faulty compressor may be indicated. A current imbal-
ance exceeding 15% of the average on the three phases
should be investigated further.
COMPRESSOR REPLACEMENT — All models contain
scroll compressors and have from one to six compressors.
38APD025-030 units utilize a single compressor per circuit.
These compressors are mounted directly to the unit base. All
other sizes have multiple compressors per circuit. Multiple
compressor circuits are mounted in sets on mounting rails.
1. Open and tag all disconnects following proper lock-out
tag-out procedures. Use proper personal protective equip-
ment.
2. Remove the junction box cover and disconnect the com-
pressor power and ground connections. See Fig. 167 or
168.
3. Disconnect and remove the crankcase heater from the
compressor. Save the ground screw for re-installation
later.
4. If the compressor is equipped with a motor protection
module (Kriwan or CoreSense), disconnect the wiring to
the device.
5. Remove the cable from the compressor junction box.
6. If the compressor is a digital compressor, remove the dig-
ital unloader solenoid (Fig. 169). Save the mounting
screw for re-installation later. Remove the harness from
the junction box.
7. Isolate the circuit and remove the refrigerant using stan-
dard refrigeration techniques.
8. If the circuit high pressure switch (HPS), discharge tem-
perature thermistor (DTT), return gas thermistor (RGT),
discharge pressure transducer (DPT), or suction pressure
transducer (SPT) are in an area where brazing could dam-
age the sensor, remove the device from the line and se-
cure it out of the way.
9. For tandem and trio compressor circuits, remove the oil
from the compressors as described in the section Remov-
ing Oil on page 149. This is required to cut (tandem com-
pressor circuits) or remove (trio compressor circuits) the
oil equalizer line. For tandem compressor circuits, cut the
oil equalizer with a tubing cutter in a convenient place to
be able to reconnect with a coupling.
10. Remove the bolts securing the compressor. Be sure to
save all of the mounting hardware for compressor instal-
lation.
WARNING
Do not supply power to unit with compressor cover
removed. Failure to follow this warning can cause a fire,
resulting in personal injury or death.
WARNING
Exercise extreme caution when reading compressor cur-
rents 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. Failure to follow this warning
can cause fire, resulting in personal injury or death.
CAUTION
Do not manually operate contactors. Serious damage to the
machine may result.
WARNING
Electrical shock can cause personal injury and death. Shut
off all power to this equipment during installation and ser-
vice. There may be more than one disconnect switch. Tag
all disconnect locations to alert others not to restore power
until work is completed.
SEE
NOTE
a38-7315
NOTE: See wire color codes in
Crankcase Heater Wiring sec-
tion, page 146.
Fig. 167 — Compressor Junction Box Without
Motor Protection Module