RUN CAPACITOR MEASUREMENT PROCEDURE

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pic1 1 RUN CAPACITOR MEASUREMENT PROCEDURE

StepExpected Result/Action
1. Turn off all power to unit. Use the capacitor discharge tool {Figure SP-8-6) to
discharge the run capacitor and any other high-voltage circuit capacitors that
may be used in the unit.
All high-voltage capacitors used in the equipment are discharged, including the
run capacitor(s).
2. Locate and disconnect the wires from the run capacitor to isolate it from the
remainder of the circuit. {Refer to the unit wiring diagram.) Inspect the
capacitor for any visible signs of damage, such as bulging or leaking.
The run capacitor is isolated from the remainder of the circuit and prepared for
measurement. If the visual inspection reveals a bulged or leaking capacitor, it
should be considered bad and must be replaced.
3. Set up the VOM/DMM to measure resistance on the R x 1,000 or R x 10,000
ohm scale. Connect the VOM/DMM across the capacitor terminals and
measure the resistance as shown in Figure SP-10-7.
VOM/DMM reading first indicates zero or a low resistance, then slowly rises
toward infinity or some high value of measurable resistance. This indicates that
the capacitor is most likely good. If it is necessary to find out the capacitor's exact
capacitance value, it must be tested further using a capacitor tester per step 5.
VOM/DMM reading goes to zero or a low resistance and stays there. This
indicates that the capacitor is shorted. Replace the capacitor.
VOM/DMM reading indicates infinity. This indicates that the capacitor is open.
Replace the capacitor.
4. If testing a run capacitor enclosed in a metal case, check for a grounded
capacitor. Set up the VOM/DMM to measure resistance on the R x 1,000 or
R x 10,000 ohm scale. Connect the VOM/DMM between each one of the
capacitor terminals and the metal case and measure the resistance.
VOM/DMM reading indicates infinity. This indicates that the capacitor is not
grounded to the case.
VOM/DMM reading indicates a measurable resistance. This indicates that the
capacitor is grounded to the case. Replace the capacitor.
5. To measure a capacitor's exact capacitance MFD value, test the capacitor
using a capacitor tester. Follow the tester manufacturer's instructions to
perform the test.
The measured value for a run capacitor should be ±10% of the value shown on
the capacitor. If the value is not within these limits, replace the capacitor.

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