Capacitor Reference Guide
Run and start capacitor sizing by compressor horsepower
Capacitor Type Identification
Run Capacitor
- • Metal oval or round shape
- • Oil-filled, silver/gray color
- • 2 terminals
- • Rated 370V or 440V AC
- • Lower µF value (5-80 µF)
Start Capacitor
- • Black cylindrical plastic
- • Electrolytic type
- • 2 terminals (bakelite top)
- • Rated 125V-330V AC
- • Higher µF value (43-850 µF)
Dual Run Capacitor
- • Larger metal oval shape
- • Oil-filled, silver/gray color
- • 3 terminals: C, HERM, FAN
- • Rated 440V AC
- • Combined value (e.g., 45+5 µF)
Quick Identification Tips
Run vs Start:
- Run = Metal, silver, oil-filled, lower µF
- Start = Black plastic, electrolytic, higher µF
Single vs Dual:
- Single = 2 terminals
- Dual = 3 terminals (C, HERM, FAN)
Run Capacitors
Continuously operates during motor run
| Compressor HP | Capacitance (µF) | Voltage |
|---|---|---|
| 1/8 - 1/6 | 4 - 6 | 370V |
| 1/5 - 1/4 | 7.5 - 10 | 370V |
| 1/3 | 10 - 15 | 370V |
| 1/2 | 15 - 20 | 370V |
| 3/4 | 20 - 25 | 440V |
| 1 | 25 - 35 | 440V |
| 1.5 | 35 - 45 | 440V |
| 2 | 40 - 50 | 440V |
| 3 | 50 - 60 | 440V |
| 5 | 60 - 80 | 440V |
Start Capacitors
Provides extra torque during motor startup
| Compressor HP | Capacitance (µF) | Voltage |
|---|---|---|
| 1/8 - 1/6 | 43 - 53 | 125V |
| 1/5 - 1/4 | 88 - 108 | 125V |
| 1/3 | 145 - 175 | 125V |
| 1/2 | 189 - 227 | 125V |
| 3/4 | 233 - 280 | 125V |
| 1 | 270 - 324 | 165V |
| 1.5 | 324 - 389 | 165V |
| 2 | 400 - 480 | 250V |
| 3 | 540 - 648 | 250V |
| 5 | 708 - 850 | 330V |
Condenser Fan Motor Capacitors
Run capacitors for outdoor fan motors
| Motor HP | Motor FLA | Capacitor (µF) | Voltage |
|---|---|---|---|
| 1/8 | 1.0 - 1.4 | 2 - 3 | 370V |
| 1/6 | 1.3 - 1.8 | 3 - 4 | 370V |
| 1/4 | 1.8 - 2.4 | 4 - 5 | 370V |
| 1/3 | 2.2 - 3.2 | 5 - 7.5 | 370V |
| 1/2 | 3.0 - 4.2 | 7.5 - 10 | 370V |
| 3/4 | 4.0 - 5.5 | 10 - 12.5 | 440V |
| 1 | 5.0 - 6.5 | 12.5 - 15 | 440V |
Capacitor Types
Run Capacitor
- Oil-filled, designed for continuous duty
- Improves motor efficiency and power factor
- Typically rated 370V or 440V AC
- Can often be replaced with higher voltage rating
Start Capacitor
- Electrolytic, designed for short-term use
- Provides high starting torque
- Must be disconnected after motor starts
- Used with potential relay or solid-state starter
Dual Run Capacitors
Dual run capacitors combine compressor and fan motor capacitors in one unit. They have three terminals: C (Common), HERM (Compressor), and FAN.
Common Dual Capacitor Ratings
| Typical System | HERM (µF) | FAN (µF) |
|---|---|---|
| 1.5 - 2 Ton | 25-30 | 5 |
| 2.5 - 3 Ton | 35-40 | 5-7.5 |
| 3.5 - 4 Ton | 45-50 | 7.5 |
| 5 Ton | 55-60 | 7.5-10 |
Safety Warning
- Always discharge capacitors before handling - they can store lethal voltage
- Use a resistor (10-20kΩ, 5W) to safely discharge capacitors
- Never replace a capacitor with a lower voltage rating
- Always verify correct polarity on electrolytic start capacitors
- When in doubt, refer to equipment manufacturer specifications