5 Signs Your AC Capacitor Is Failing (And How to Replace It)

June 28, 2026 • CORALVU LIMITED COMPANY

Your AC Unit Won't Start? It Might Be the Capacitor.

The capacitor is one of the most common failure points in residential and commercial HVAC systems. It stores and releases electrical energy to start and run the compressor and fan motors. When it fails, your system either won't start or will run inefficiently — driving up your electric bill.

Here are the five warning signs to watch for:

1. The AC Hums But Doesn't Start

If you hear a humming sound from the outdoor unit but the fan doesn't spin, the start capacitor has likely failed. The motor needs that initial jolt of energy to get spinning — without it, it just hums and overheats.

2. Your Electric Bill Suddenly Spikes

A weak capacitor forces the motor to draw more current to compensate. This increased draw shows up directly on your utility bill. If your usage jumped 15-20% without explanation, check your capacitor.

3. The Unit Shuts Off Randomly

Short cycling — when your AC starts and stops frequently — often points to a failing run capacitor. The system starts fine but can't maintain the charge needed to keep running.

4. You See a Swollen or Leaking Capacitor

Physical damage is the clearest sign. If the top of the capacitor is bulging (it should be flat) or you see oily residue, it's dead and needs immediate replacement.

5. The System Is More Than 5 Years Old

Capacitors in hot climates (like Texas) typically last 3-7 years. If you're in that window and experiencing any of the above symptoms, it's almost certainly the capacitor.

How to Replace It

Replacing an AC capacitor is a 15-minute job if you're comfortable with basic electrical work:

  1. Turn off power at the breaker AND the disconnect box
  2. Discharge the old capacitor (use an insulated screwdriver across the terminals)
  3. Photo the wiring before disconnecting
  4. Match the specs exactly: voltage (370V or 440V) and microfarads (MFD)
  5. Connect wires to matching terminals on the new capacitor
  6. Restore power and test

Pro tip: Always replace with a 440V capacitor even if the original was 370V — 440V is backwards compatible and lasts longer in extreme heat.

Get the Right Part

CoralVolt dual run capacitors are UL certified, rated for 440/370V, and built for extreme US weather conditions. Direct-fit replacement for all major brands including Carrier, Trane, Lennox, and Goodman.