AC Capacitor Replacement: Complete DIY Guide 2026

Your AC capacitor just failed, and you got quoted $250-400 for replacement. The part costs $15-30. Here's how to replace it yourself in 30 minutes and save $150-350.

What You'll Need

Tools Required:

• Insulated screwdriver (MUST be insulated)
• Needle-nose pliers
• Smartphone camera (to photograph wiring)
• Nut driver or socket set (usually 5/16" or 1/4")

Safety Equipment:

• Insulated gloves (recommended)
• Safety glasses

Parts Needed:

• New capacitor (EXACT same MFD rating as old one)
• Cost: $15-40 on Amazon/SupplyHouse

How to Identify a Bad Capacitor

Symptoms:

• Outdoor unit won't start (indoor unit works fine)
• Humming or buzzing sound from outdoor unit
• Unit struggles to start, then runs fine
• Outdoor fan not spinning

Visual inspection signs:

• Bulging top (like a soda can ready to burst)
• Leaking fluid
• Rust or corrosion
• Burn marks

Step-by-Step Replacement Guide

Step 1: Turn Off ALL Power

This is the most critical step. Turn off power in TWO places:

1. At the circuit breaker: Flip the AC breaker to OFF
2. At the outdoor disconnect: Pull the disconnect block or flip the switch near your outdoor unit

Verify power is off: Try to turn on your AC at the thermostat. Nothing should happen.

Step 2: Remove Access Panel

Remove the screws or fasteners holding the access panel on your outdoor unit. Keep track of screws.

Step 3: Locate the Capacitor

The capacitor is a cylindrical metal component, usually silver or black, about the size of a D-battery or Red Bull can.

It will have 2-3 terminals on top with wires connected.

Step 4: Take Photos of EVERYTHING

Before touching ANY wires, take multiple clear photos showing:

• All wire connections and their positions
• Terminal labels (HERM, FAN, COM or C)
• Capacitor rating (printed on side)
• Overall view of unit interior

These photos are your safety net. You'll reference them during reassembly.

Step 5: Discharge the Capacitor

How to discharge safely:

1. Using an insulated screwdriver, touch the metal shaft across BOTH terminals simultaneously
2. You may see a small spark — this is normal
3. Repeat 2-3 times to ensure full discharge
4. For dual capacitors (3 terminals), discharge between:
   • HERM and COM
   • FAN and COM

Step 6: Disconnect Wires

Once discharged, disconnect wires one at a time:

1. Note which wire goes to which terminal
2. Gently pull wire terminals off (don't pull on wires themselves)
3. Some terminals use screws — loosen these

Wire identification for dual capacitors:

• HERM (or H): Compressor wire
• FAN (or F): Fan motor wire
• COM (or C): Common wire (usually 2 wires here)

Step 7: Remove Old Capacitor

The capacitor is held by a metal band or bracket. Remove the mounting hardware and take out the old capacitor.

Step 8: Match Exact Specifications

Check the label on your old capacitor. You need to match:

• MFD rating: This is critical (e.g., 35+5 MFD or 45+5 MFD)
• Voltage rating: Usually 370V or 440V
• Single or dual: Dual capacitors have 3 terminals

Step 9: Install New Capacitor

1. Mount new capacitor in bracket (same orientation as old one)
2. Tighten mounting hardware

Step 10: Reconnect Wires

Using your photos as reference:

1. Connect each wire to its proper terminal
2. Push terminal connectors firmly onto posts
3. Ensure connections are tight and secure
4. Double-check against your photos

Common dual capacitor wiring:

• HERM terminal: Brown wire from compressor
• FAN terminal: Wire from fan motor
• COM terminal: Two wires (usually from contactor)

Step 11: Replace Access Panel

Reinstall the access panel with all screws.

Step 12: Restore Power and Test

1. Reinstall outdoor disconnect block
2. Turn on circuit breaker
3. Go to thermostat and turn on cooling
4. Listen for outdoor unit to start
5. Verify both compressor and fan are running
6. Check for cool air from vents

Troubleshooting

Unit Still Won't Start:

• Verify all wires are connected properly
• Check that you got the correct replacement capacitor
• Problem may be the contactor or compressor (call professional)

Fan Runs But Compressor Doesn't:

• Check HERM terminal connection
• Compressor may be bad (separate issue)

Neither Fan Nor Compressor Runs:

• Verify power is on at both breaker and disconnect
• Check thermostat settings
• May be contactor or other electrical issue

Where to Buy Capacitors

• Amazon: Fastest delivery, 2-day shipping with Prime
• SupplyHouse.com: HVAC specialty supplier, great selection
• Local HVAC supply: Same-day pickup, but may not sell to public
• Home Depot/Lowe's: Limited selection, often overpriced

Cost comparison:

• Online: $15-30
• Local supply house: $25-45
• Home Depot: $30-60
• Contractor markup: $75-200

How Much Money You'll Save

Contractor pricing breakdown:

• Service call: $75-150
• Diagnostic: $0-100 (sometimes waived)
• Parts (their cost): $15-30
• Parts (their charge): $75-200
• Labor: $100-200
• Total: $250-450

DIY cost:

• Capacitor: $15-40
• Time: 30-60 minutes
• Total: $15-40

Savings: $210-410 for 30-60 minutes of work

When to Call a Professional Instead

Don't attempt this DIY if:

• You're not comfortable with basic electrical work
• Your system is still under warranty (DIY may void it)
• The capacitor looks normal (problem is elsewhere)
• You've replaced the capacitor but unit still doesn't work
• There are signs of extensive electrical damage

Preventive Maintenance

Capacitors typically last 10-20 years but can fail sooner in hot climates. To extend life:

• Keep outdoor unit clean and clear of debris
• Ensure adequate airflow around unit
• Schedule annual professional maintenance
• Don't run AC with dirty filters

Bottom Line

Replacing an AC capacitor is one of the best DIY repairs for homeowners comfortable with basic electrical work. It's:

• Quick: 30-60 minutes
• Inexpensive: $15-40 in parts
• High savings: $210-410 vs. contractor
• Straightforward: Follow steps carefully

Just remember: safety first. If you're unsure at any step, call a professional.

More DIY Guides

Ready to tackle more AC repairs yourself? Check out our other guides:

• Complete DIY AC Repair Guide — 5 repairs that save $1000+
• Fix Your AC Yourself — Step-by-step for common issues
• AC Repair Cost Guide — Know fair pricing