Compressor Troubleshooting

52C,P

SERIES

The rotary compression process (Figure 28), 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 piston moves to position A as shown in (2). The suction volume is now the area defined by point A and the tip of the vane. Gas in the remaining volume has been compressed above suction pressure. After another

90 degrees of shaft rotation, the rolling piston has moved to position B as shown in (3). Both the com- pressed 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. Contin- uous suction and discharge allows for a smooth com- pression process.

The rolling piston is not in actual contact with the cyl- inder wall, vane, or bearing faces. Hydrodynamic seal- ing prevents leakage from the compressed gas volume to the suction volume via these paths. Precise control of machining tolerances, surfaces, finishes, and assem- bly clearances is critical to achieve high efficiency per- formance. In addition, the line contact between the vane tip and the rolling piston requires careful selec- tion and control of materials to provide wear resis- tance and reliable long-term operation.

Refer to Figure 29 for a basic compressor troubleshoot- ing chart.

FIGURE 28 — ROTARY COMPRESSOR

COMPRESSION PROCESS

BASIC HERMETIC COMPRESSOR ELECTRICAL MEASUREMENTS

There are 2 basic electrical tests for hermetic compres- sors that will determine the electrical state of the motor. 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 UNIT DISASSEMBLY section.

3.Open the control box as detailed in the UNIT DISASSEMBLY section, then locate, label, and remove the 3 compressor wires from the following locations: the RUN wire (BLACK) from the capac- itor, the START wire (BLUE) from the capacitor. The third wire, COMMON wire (YELLOW) may be connected to one of the following locations: for PC units the wire is on the indoor thermostat, for CE, PE Remote Control Units the wire is on the RC Control Board, for all other CE, PE Units the wire is located on the rotary selector switch. For ALL CQ, PQ Units the wire is on the outdoor frost thermostat.

For compressors that are known to be dam- aged: Remove refrigerant prior to disconnecting compressor 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 removing compressor wires.

4.Perform a shorted/open windings test to measure the resistance between the windings of the com- pressor 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 30. 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 winding to winding.

NOTE: The rotary compressor has the compressor overload located under the terminal cover. If the over- load is open it can show ohm readings that are infinite. The unit should be off for at least an hour to give this overload time to reset if it is open.