Figure 14-40. - Testing a starting relay with an ohmmeter.
The equipment and procedures for testing circuit components such as starting relays, overload protectors, and capacitors are discussed as follows.
Starting relays can be tested two ways with an ohmmeter. The meter can be used to check across the relay contacts, or it can be used to check across the relay coil. This does not apply to thermal relays. Figure 14-40 illustrates procedures for these tests.
When you check the relay contacts, you must know if the contacts are normally open or normally closed. Voltage relay contacts and thermal relay contacts are normally closed, whereas current relay contacts are normally open. The meter reading should indicate continuity through voltage and thermal relays since the contacts are normally closed. On the other hand, if the meter indicates continuity through the normally open contacts of a current relay, the contacts are probably fused together.
Another method of checking starting relays is by using a test line cord and fuse combination to isolate the relay. Figure 14-41 illustrates the procedure used in making this test. Obtain a capacitor of the approximate size used with the compressor motor. Connect it from the hot side of the running winding to the hot side of the starting winding. Connect the test line to the motor terminals as illustrated in the figure and plug it in. If the compressor is good it should start running. After a short time, disconnect the capacitor. The compressor should continue to speed up and run normally. This procedure has accomplished manually what a properly functioning starting relay is supposed to accomplish. If the motor failed to start normally before the check, the relay is bad.
Voltage and current relay coils can also be tested for resistance with an ohmmeter. When the coil is burned out, the meter indicates no resistance or an open coil. Commercial starting relay testers are available from several manufacturers.
Questionable Klixon external overload protectors should be replaced with new ones. If the
Figure 14-41. - Procedures for checking a starting relay with a test line.Continue Reading