Service manual

SERVICING
32
2. Identify the leads and using a Megger, Hi-Potential
Ground Tester, or other suitable instrument which puts
out a voltage between 300 and 1500 volts, check for a
ground separately between each of the three leads and
ground (such as an unpainted tube on the compres-
sor). Do not use a low voltage output instrument such
as a volt-ohmmeter.
3. If a ground is indicated, then carefully remove the com-
pressor terminal protective cover and inspect for loose
leads or insulation breaks in the lead wires.
4. If no visual problems indicated, carefully remove the
leads at the compressor terminals.
Carefully retest for ground, directly between compres-
sor terminals and ground.
5. If ground is indicated, replace the compressor.
S-17C Operation Test
If the voltage, capacitor, overload and motor winding test
fail to show the cause for failure:
WARNING
Disconnect Electrical Power Supply:
1. Remove unit wiring from disconnect switch and wire a
test cord to the disconnect switch.
NOTE: The wire size of the test cord must equal the line
wire size and the fuse must be of the proper size and type.
2. With the protective terminal cover in place, use the three
leads to the compressor terminals that were discon-
nected at the nearest point to the compressor and con-
nect the common, start and run clips to the respective
leads.
3. Connect good capacitors of the right MFD and voltage
rating into the circuit.
4. With power ON, close the switch.
WARNING
LINE VOLTAGE NOW PRESENT
A. If the compressor starts and continues to run, the
cause for failure is somewhere else in the sys-
tem.
B. If the compressor fails to start - replace.
Compressor Serial Number Identification
COPELAND COMPRESSOR
E · 93 J 123456
Motor Shift Year Month Serial No
TECUMSEH COMPRESSOR
T:
G 22 93C 123456
Month Day Year Serial No
Day of
Year
Year Serial No
BRISTOL COMPRESSOR
291 93 123456
S-18 TESTING CRANKCASE HEATER
The crankcase heater must be energized a minimum of
four (4) hours before the condensing unit is operated.
Crankcase heaters are used to prevent migration or accu-
mulation of refrigerant in the compressor crankcase during
the off cycles and prevents liquid slugging or oil pumping
on start up. Scroll Compressors are not equipped with a
crankcase heaters.
A crankcase heater will not prevent compressor damage
due to a floodback or over charge condition.
WARNING
Disconnect Electrical Power Supply:
1. Disconnect the heater lead wires.
2. Using an ohmmeter, check heater continuity - should
test continuous, if not, replace.
NOTE: The positive temperature coefficient crankcase
heater is a 40 watt 265 voltage heater. The cool resistance
of the heater will be approximately 1800 ohms. The resis-
tance will become greater as the temperature of the com-
pressor shell increases.
S-21 CHECKING REVERSING VALVE AND SOLE-
NOID
Occasionally the reversing valve may stick in the heating
or cooling position or in the mid-position.
When stuck in the mid-position, part of the discharge gas
from the compressor is directed back to the suction side,
resulting in excessively high suction pressure. An increase
in the suction line temperature through the reversing valve
can also be measured. Check operation of the valve by
starting the system and switching the operation from COOL-
ING to HEATING cycle.