TESTING MOTOR WINDINGS

If, during the procedure for identifying motor terminals, the ohmmeter displays a blank readout during any test, there is probably a defective winding. A defective winding may be classified as an OPEN winding or a SHORTED winding. The display will be zero if the winding is GROUNDED. Test equipment and procedures applicable to faulty windings are discussed below.

OPEN WINDINGS

Open windings can occur in the starting winding, the running winding, or both. An open winding is the result of a burned-out or grounded fault or simply a break somewhere in the lead or winding that prevents the current from completing the circuit. A motor with an open winding does not start. If only one winding is open, the motor hums, but if both windings are open, no sound is emitted nor current consumed. Open windings can be checked by an ohmmeter, a voltmeter, or a test light.

Ohmmeter Continuity Test Procedure

The procedure for making an ohmmeter continuity test is shown in figure 14-31 and outlined below.

Turn the power OFF, discharge all capacitors, and remove the wires from the C-, S-, and R-terminals of the motor.

With the ohmmeter set on the lowest scale, check the resistance from C to R, C to S, and R to S.

Table 14-30.-Electrical Troubleshooting Loads 14-18(F)

Table 14-30(B).-Testlng Controls and Paths 14-18(G)

Figure 14-31.-Testing for an open winding with a ohmmeter.

Watch the digital readout in the meter as the check is made. Each reading should appear to be approximately 0 ohms, since winding resistance is usually less than 10 ohms. If, during the check, the resistance digital display remains blank (infinity), an open or break exists.

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