Capacitor Check Calculator
Check a run capacitor under load: measured amps and volts in, microfarads and a pass/fail out.
How it works
µF = (2652 × amps) ÷ volts
At 60 Hz, a capacitor's current is proportional to its capacitance and the voltage across it. 2652 is 1,000,000 ÷ (2π × 60). Testing under load shows how the capacitor performs at operating voltage, which a meter's capacitance setting can miss.
How to take the readings
- With the unit running, clamp the wire between the capacitor and the motor's start (aux) winding.
- Measure voltage across the capacitor terminals for that motor (Herm to C, or Fan to C).
- For a dual capacitor, check each side separately against its own rating.
- Capacitors store a charge. Discharge before handling, and keep hands clear of terminals while the unit runs.
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Results are estimates for field reference. Always confirm against the equipment manufacturer's charging chart, installation instructions and local code. Found a problem with this tool? Tell us.