How do you tell if a capacitor needs to be replaced?

Author: Mckayla Lind  |  Last update: Thursday, July 3, 2025

One of the most common signs of a failing AC capacitor is an overly warm home. Without this component, the cooling cycle won't start and indoor temperatures won't go down. Other signs of capacitor problems include: Loud humming sounds coming from the AC condenser.

How to test if a capacitor is bad?

A good capacitor will show a low resistance when discharged and the reading slowly rises to infinity in time as it charges up to the multimeter battery voltage and stays there. A leaky capacitor will show a reading less than infinity and will never reach that level. A short circuit well that is self explanatory.

What are the symptoms of a bad capacitor?

A bad capacitor in a circuit can cause various problems. It may fail to store and release energy properly, leading to unstable voltage, poor performance, or complete circuit failure. Symptoms include power surges, overheating, or malfunctioning parts, potentially damaging other components over time.

Will AC still run with a bad capacitor?

If the start capacitor malfunctions or wears out, it usually prevents the HVAC unit or the blower from turning on. A bad run capacitor won't prevent the unit from starting, but it can lead to the unit shutting down prematurely, overheating or making more noise than usual.

When should a capacitor be replaced?

The capacitor is one of the parts you should expect to replace at some point in your AC's lifetime. While your AC itself could last for 15 years, the capacitor won't last that long. It might make it five years before you need to replace the capacitor. In some systems, there are multiple capacitors.

How to Measure Capacitance without Desoldering Capacitors from a PCB

Can I replace an AC capacitor myself?

Since AC capacitors are high-voltage components that might cause significant injury to you even if the power is out, it is strongly recommended against changing them yourself. Follow any instructions provided with your new unit purchase if you're thinking about replacing your own AC capacitor filter.

What is the average lifespan of a capacitor?

Over time, capacitors degrade due to normal wear and tear. When combined with heat exposure, a capacitor's average life span of 20 years can plummet. Improper voltage.

How do I know if I need a new AC capacitor?

How To Recognize a Failing AC Capacitor
  1. Loud humming sounds coming from the AC condenser.
  2. Having your air conditioning shut off without warning.
  3. Burnt odors or smoke coming from the outdoor condenser.

What kills an AC capacitor?

These are some of the factors that may be affecting the lifespan of AC capacitors: Heat exposure: Heat may be one of the most damaging elements for air conditioner capacitors. Exposing these units to high heat for extended periods shortens their lives and can cause significant damage to your unit.

Will the fan work if the capacitor is bad?

Now, you know the answer to, “Will an AC fan run if the capacitor is bad?” It will run for a while (although not with the appropriate energy efficiency or cooling capacity) but will eventually keep your unit from turning on and functioning altogether.

How to test an air conditioning capacitor?

Test the Capacitor

Set your multimeter to the capacitance setting (often indicated by a symbol like “MFD" or “μF”). Place the multimeter probes on the capacitor terminals. The multimeter will display a reading. Compare this reading to the rated capacitance value printed on the capacitor.

Which is the most common reason for capacitor failure?

DIELECTRIC BREAKDOWN (SHORTS)

The classic capacitor failure mechanism is dielectric breakdown. The dielectric in the capacitor is subjected to the full potential to which the device is charged and, due to small capacitor physical sizes, high electrical stresses are common.

Will a motor hum if the capacitor is bad?

A faulty capacitor – whether it's the wrong size, blown, or damaged – can be the root cause of your motor hum. Solution: Test and replace any faulty capacitors. Both the start and run capacitors are usually located on the exterior of the motor housing, often in dedicated metal or plastic casings.

What happens when you have a bad capacitor?

A bad capacitor forces the motor to work harder than usual, leading to overheating and a burning smell. However, you may fail to notice the electrical odor because the capacitor sits outside. If your air conditioner isn't working, look at the condenser unit to ensure the motor isn't overheating.

Can I test a capacitor without removing it?

To perform a check on a capacitor while it is still installed in a circuit, an ESR meter will be necessary. If the capacitor is removed from the circuit then a multimeter set as an ohm meter can be used, but only to perform an all-or-nothing test. This test will only show if the capacitor is completely dead, or not.

How to tell if a fan motor or capacitor is bad?

Signs a Fan Motor or Capacitor Is Bad
  1. Fan Starts, But Only After a Delay. Demonstrates that the fan is operable, but underpowered.
  2. Motor Hums But Won't Start. Indicates electricity is flowing into the unit, but it doesn't have enough power to start up.
  3. Loud or Unusual Noises. ...
  4. Fan Runs Intermittently.

Can I run my AC with a bad capacitor?

Although your unit may continue to run, it is not wise to continue using the air conditioner before replacing a failing capacitor as it can lead to compressor failure and fan motor issues as well as system failure.

How much does it cost to replace a capacitor in an air conditioner?

For AC capacitor replacement, anticipate spending between $150 and $400, depending on the capacitor's type and accessibility. A bad AC capacitor is a fairly minor repair, and most HVAC technicians will recommend a repair rather than replacing the unit when the capacitor is the problem.

Will a motor run with a bad capacitor?

If the capacitor fails open circuit you probably won't be able to get the motor running, though sometimes they will go (probably at lower speed/power) if you can spin the shaft. And amusingly, they may fail to a wrong value and allow the motor to run backwards.

What is the most common part to fail on an AC unit?

#1 Most Common Air Conditioning Repair – Bad Capacitor

The fan of course makes a whirring noise, the compressor is like a deep buzz like a refrigerator running. Holding your hand above the fan should feel warmer than the outside air.

Is replacing AC capacitor easy?

Can You Replace an AC Capacitor Yourself? Replacing a capacitor is a relatively simple task that most people can do themselves with a little bit of research. However, it is important to remember that capacitors store a lot of energy, so it is necessary to discharge the capacitor before working on it.

Can AC run without a capacitor?

When you switch on your AC, numerous components work together to cool your space effectively. Among these, capacitors play a crucial role. These components are essential for powering your air conditioner, enabling it to operate efficiently. Without capacitors, your system simply couldn't function.

How do you know if a capacitor is gone?

How to test a bad capacitor? Connect the multimeter probes to the capacitor and set it to capacitance mode. Then, take the value and compare it to the expected value of the capacitor. If it is within 10-20% it is good, if not, it is bad.

Can capacitors last 40 years?

40 years is not uncommon for good capacitors kept cool, but it's also possible some have excessive ESR. It's usually not a catastrophic failure, just an increase in ESR (equivalent series resistance) as the electrolyte dries out.

Previous article
What should I set my heat pump to in winter?
Next article
Can your home AC run out of Freon?