Capacitor Sizing Calculator
Calculate Run, Start & Dual Capacitor Values
Run Capacitor Calculator
Calculate run capacitor size based on motor specifications or electrical measurements.
Start Capacitor Calculator
Calculate start capacitor size for hard-start applications.
Dual Capacitor Selector
Find the right dual capacitor for compressor + fan motor combination.
How to Test a Capacitor
Using a Multimeter
- 1 Disconnect power and discharge capacitor using a resistor (20kΩ, 5W)
- 2 Set multimeter to capacitance mode (F)
- 3 Connect leads to capacitor terminals
- 4 Reading should be within ±6% of rated value
Signs of Bad Capacitor
- Bulging or swollen top - Replace immediately
- Oil leaking - Internal failure
- Burn marks - Overheated
- Reading more than 6% low - Weak capacitor
- No reading (OL) - Open or failed
Quick Reference
Run Capacitor
- • Continuous duty (always in circuit)
- • Oil-filled, oval or round shape
- • Typical: 5-80 µF
- • Voltage: 370V or 440V AC
Start Capacitor
- • Intermittent duty (start only)
- • Electrolytic, black plastic case
- • Typical: 88-1000 µF
- • Voltage: 125V or 250V AC
Dual Capacitor
- • Two run caps in one package
- • 3 terminals: C, HERM, FAN
- • Common in residential AC
- • Replace with exact match
Replacement Guidelines
- µF rating: Match exactly or within ±10%
- Voltage: Same or higher rating OK
- Type: Never swap start for run
- Size: Physical size can differ
Common Capacitor Sizes
| Tons | Run µF | Start µF |
|---|---|---|
| 1.5 | 25-30 | 88-108 |
| 2 | 30-35 | 108-130 |
| 2.5 | 35-40 | 145-175 |
| 3 | 40-45 | 189-227 |
| 3.5 | 45-50 | 233-280 |
| 4 | 50-55 | 270-324 |
| 5 | 55-60 | 340-408 |
Values for 230V single phase. Actual values may vary by manufacturer.