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The rotary compression process (Figure 33), starts at
top dead center as shown in (1). Suction gas flows
through the suction inlet and into the cylinder area. As
the shaft rotates through 90 degrees, the rolling pis-
ton moves to position A as shown in (2). The suction vol-
ume is now the area defined by point A and the tip of
the vane. Gas in the remaining volume has been com-
pressed above suction pressure. After another 90 degrees
of shaft rotation, the rolling piston has moved to posi-
tion B as shown in (3). Both the compressed gas and
suction gas volumes are now equal. Another 90 degrees
of shaft rotation is shown in (4). Compressed gas has
reached a pressure sufficient to open the discharge valve,
and flows from the cylinder into the compressor shell.
After another 90 degrees of shaft rotation, the entire
process begins again. Continuous suction and discharge
allows for a smooth compression process.
The rolling piston is not in actual contact with the cyl-
inder wall, vane, or bearing faces. Hydrodynamic
sealing prevents leakage from the compressed gas vol-
ume to the suction volume via these paths. Precise con-
trol of machining tolerances, surfaces, finishes, and
assembly clearances is critical to achieve high efficiency
performance. In addition, the line contact between the
vane tip and the rolling piston requires careful selection
and control of materials to provide wear resistance and
reliable long-term operation.
COMPRESSOR TROUBLESHOOTING
Refer to Figure 34 for a basic compressor troubleshoot-
ing chart.
BASIC HERMETIC COMPRESSOR
ELECTRICAL MEASUREMENTS
There are 2 basic electrical tests for hermetic compres-
sors that will determine the electrical state of the mo-
tor. The first test requires checking the electrical
resistance of each of the electrical motor windings. The
second test requires checking the electrical resistance
of each of the electrical motor windings to ground. These
tests may be accomplished by performing the following
steps:
1. DISCONNECT ALL POWER TO THE UNIT.
2. Remove the unit chassis from the sleeve as detailed
in the GENERAL DISASSEMBLY section.
3. Open the control box as detailed in the GENERAL
DISASSEMBLY section, then locate, label, and re-
move the 3 compressor wires from the following loca-
tions: the RUN wire (BLACK) from the capacitor,
the START wire (BLUE) from the capacitor. The third
wire, COMMON wire (YELLOW) may be connected
to one of the following locations: for SC units the
wire is on the indoor thermostat, for SE Remote
Control Units the wire is on the indoor frost ther-
mostat, for all other SE Units the wire is located
on the push button switch, for ALL SQ Units the
wire is on the outdoor frost thermostat.
For compressors that are known to be dam-
aged: Remove refrigerant prior to disconnecting com-
pressor wires. Damaged hermetic compressor
terminals may become loose and eject from the com-
pressor. Wear safety glasses and keep your face
away from the area above the terminals when remov-
ing compressor wires.
4. To measure the resistance between the windings of
the compressor motor, use a volt-ohmmeter set to
the lowest ohm reading level then read and record
the resistance between the RUN and START, START
and COMMON, and RUN and COMMON wires.
See Figure 35. The typical resistance readings will
be about 4, 3, and 1 ohms respectively. The smaller
values should add to equal the larger value. If this is
not true then the compressor is likely shorted wind-
ing to winding.
NOTE: The rotary compressor has the compressor over-
load located under the terminal cover. If the overload
is open it can show ohm readings that are infinite. The
unit should be off for at least an hour to give this over-
load time to reset if it is open.
FIGURE 33 — ROTARY COMPRESSOR
COMPRESSION PROCESS
17