How to Troubleshoot and Replace AC Capacitor

AC capacitors are vital components of the air conditioning system. They provide the AC motors with the necessary torque to start and run optimally. That helps the AC components to not only be efficient but also last long.

replacing and air conditioner capacitor

A bad AC capacitor is however trouble for your air conditioner. If you don’t replace it early enough it can cause other AC parts to fail as well, resulting in expensive repairs.

What a bad AC capacitor does is that it causes the compressor and fan motors to worker harder than they need to in an attempt to cool the house. That causes the motor windings to overheat and ultimately burn out.

To replace an AC capacitor, turn off power to the AC unit at the breaker box and turn off thermostat. Remove the condenser unit’s side panel, locate and discharge the capacitor. Disconnect the old capacitor and replace it with another one of the same rating.

Replacing and AC capacitor is not hard and you can do it on your own. However, capacitors store a high electric charge and can shock you if they are not properly discharged. If you are not trained or have no experience working with electricity, have a licensed HVAC technician replace it for you.

Capacitors cost about $10-20, which is what you will spend if you replace it yourself. However, it will cost you between $100 and $400 to have an HVAC technician replace the capacitor for you, depending on where you live.

Although some air conditioners can still run with a bad capacitor, doing so isn’t recommended. Not only will that increase your energy bills but it will also cause the air conditioner to overwork/strain causing premature failure and therefore more expensive repairs.

An AC can have a start and a run capacitor. However, most air conditioning system will have only a run capacitor. It could be either 2 single run capacitors or one dual run capacitor. More on that later.

In this post, I will educate you on how to safely and correctly troubleshoot and replace an air conditioner run capacitor.

Troubleshooting an Air Conditioner Capacitor

dual run ac capacitor

There are 3 ways you can tell if your air conditioner capacitor is blown. They include:

  • Telltale signs exhibited by the air conditioner
  • Visually inspecting the capacitor
  • Testing the capacitor’s capacitance.

So what are the telltale signs that your air conditioner capacitor is out? The following are some of the signs of a bad AC capacitor:

  • The air conditioner will not turn on at all – The capacitor provides the compressor motor with startup torque needed to start. If the capacitor is bad, the air conditioner may not come on at all.
  • Air conditioner is hesitating before coming on – Does your air conditioner take longer to come on than usual? That could be a sign that the capacitor is not providing the motor with torque need to start promptly and hence the reason it takes too long to come on.
  • Outside unit is making humming noises – If the capacitor has failed, it will not deliver the powerful electricity jolt needed by the motor. As a result, every time the thermostat calls for cooling, the motor will strain as it tries to kick in and hence the humming sounds.
  • Burning smell from the outside unit – Is there a burning smell from the AC outside unit? That is another sign of a bad capacitor. Since the capacitor cannot quickly start the motor, the motor strains to start which causes it to overheat and hence the burning smell.
  • Fan not spinning – If the AC is running but when you peep through the top of the outside unit you notice that the fan is not spinning, the capacitor could be out. Just to be sure, use a long screwdriver or a thin stick to manual turn the fun blades (clockwise) through the grille. If the fan starts running properly, the capacitor has failed.
  • High power bills – As you can imagine, without the capacitor supplying the AC motors with the needed torque to start and run, the motors will need to draw a lot of power from the line and also run for longer. For that reason, you will notice an increase in your energy bills at the end of the month.
  • AC Shuts off randomly – A bad capacitor can cause the AC to short cycle. Run capacitors maintain an even and sufficient supply of current to the motor’s circuit. If the capacitor is bad, the circuit will not receive enough current to keep it running forcing it to turn on and off randomly.

The thing with air conditioners is that different problematic issues will often have the same symptoms. For instance, if your conditioner has not have the air filter changed or if the refrigerant levels are low, it will have the same problems as some of the ones I have outlined above.

For that reason, the best way to tell if you have a bad AC capacitor is by testing it. Visually inspecting the capacitor can also help you know if the capacitor is bad.

I will combine the process of testing the capacitor with steps to take when replacing the capacitor in the section below.

How to Replace an Air Conditioner Capacitor

To test and replace an air conditioner capacitor, you will need the following:

  • Screwdriver with an insulated handle
  • Multimeter
  • Insulated gloves
  • A new capacitor
  • Needle-nose pliers (optional)

The following are the steps to follow when replacing an air conditioner’s capacitor:

Step 1: Turn off Power to the AC

There will be 240 volts flowing to the AC unit outside your house (that is where the run capacitor is located). To work safely, you need to first make sure that no power is being supplied to the unit.

There are 2 ways to do that. In most cases, there will be a break box next to the condenser unit mounted on the wall with a lever/switch. That is where you turn off the power from. In some causes you will need to pull out a plug.

ac breaker box

If you don’t have that setup, go inside your house where the main electric panel is and look for the circuit breaker labeled “air conditioner” or simply “AC”. Pull the double bar (each 120 volts) to the off position.

Even though the power is now turned off, some voltage will still flow to the unit when the thermostat calls for cooling. For that reason, make sure to also turn off the thermostat.

Step 2: Remove the Side Panel

Now that it is safe to work on the condenser unit, you can go ahead and start by removing the side panel. The side panel conceals the capacitor and other electrical components like the contactor or hard start kit.

It will be on the side of the unit secured using 4 screws. Use the screwdriver to remove the panel/cover and expose the capacitor.

Step 3: Inspect the Capacitor

As I had mentioned earlier, it is possible to tell if your air conditioner is bad by just having a look at it. There are signs which will let you know that the AC capacitor is bad and you don’t even need to test it.

These are things you can do without even touching the capacitor which I don’t recommend doing at this stage since it is yet to be discharged.

First, look at the shape of the capacitor. Is it swollen or bulging, unlike the usual nice cylindrical shape from top to bottom?

To be precise, has the top part of the capacitor mushroomed? If the capacitor looks deformed, it is clearly bad and will need to be replaced.

Another sign that the capacitor is bad is if it is leaking out the dielectric fluid. Capacitors are filled with a fluid/oil to prevent them from overheating. If the capacitor fluid is leaking, you don’t need to test it. It is bad.

It is important to note that the capacitor could still be bad and still not exhibit the signs indicated above. That is why testing is important.

Step 4: Discharge the Capacitor

discharging and ac capacitor
How to discharge a capacitor using a screwdriver

This is the point where you want to wear your gloves and use your screwdriver to remove any charge stored by the capacitor by short-circuiting the terminals.

First determine if you have a single or dual capacitor. The process of discharging them is different. Also, ensure that you are grabbing the insulated screwdriver handle and not the metal part.

If you have a single run capacitor, place the tip of the screwdriver on the positive terminal and then short the capacitor by also making contact with the negative terminal, using the screwdriver metal part as well.

If you have a dual run capacitor, use the screwdriver to short the COMMON and HERM terminal and then COMMON and FAN terminals to discharge it.

That is how easy it is to discharge a capacitor.

Step 5: Disconnect the Capacitor

Before you can disconnect the capacitor, take your time to notice how the wires are connected to the capacitor. That is how you will connect them to the new capacitor. Taking a picture or video with your phone is an excellent idea.

Use the pliers to disconnect the wires from the capacitors. The capacitor will also be secured to the unit using a strap. Undo the strap as well.

Place the capacitor on working table where you can test the capacitance using a multimeter.

Step 6: Test the Capacitor

This step is optional. If you have decided that your capacitor is bad you don’t need to test it. You can go ahead and just install the new one. This step is necessary if you want to find out if indeed your capacitor is bad or your AC problem is being caused by something else.

A capacitor has 2 ratings which are voltage and capacitance. In this test, we are interested in capacitance, which describes the amount of charge that the capacitor can accumulate or store.

If you look on your old capacitor, you can clearly see the capacitance indicated in uF (microfarads). You will see another figure next to it (usually 6%) which means that the needed capacitance is less or more than 6% of the value indicated.

Dual run capacitors will have 2 values, something like 45/5 uF. The large value is for the compressor while the lower value is for the fan motor.

To test capacitance in you capacitor, start by having your multimeter dial in the capacitance setting (MFD/uF).

With a single run capacitor, put the multimeter probes on the 2 terminals and then note down the capacitance reading.

If you have a dual run capacitor, place one probe on the COMMON terminal and the other on the HERM terminal. Note down the readings. Next place the probes on COMMON and FAN terminals and not down the reading as well.

If for example you have a dual run capacitor rated 45/5 uF +/-6%, the allowed range of capacitance is 4.7-5.3 microfarads for the fan side of the capacitor and 42.3-47.7 microfarads on the compressor side of the capacitor.

If your readings fall out of this range, your capacitor is clearly bad and you will need to replace it.

So, what if you find out that in dual run capacitor, the compressor side is good but the fan side is bad or vice versa? You will still need to replace the capacitor. You need both sides of the capacitor to be good.

Step 7: Replace the Capacitor

Needless to say, a bad capacitor will need to be replaced. It is however extremely important to make sure that you replace the capacitor with another one of the same rating as the old one.

AC manufacturers conducts extensive tests to determine which capacitor will work well with which AC motor. That helps the AC motors to start and running seamlessly and efficiently too.

Also, don’t buy the cheapest capacitor you can find. Try to buy a quality one and from a reputable manufacturer.

Once you have the needed capacitor, proceed to install it using the same steps as when you were removing the old one, but in reverse. Be careful to make sure that you connect the correct wires to the correct terminals.

Put back the side panel as well and turn the power to the unit back on. Don’t forget to also turn on the thermostat. Give your air conditioner time and check how well it cools.

And basically that is how to replace an air conditioner run capacitor. As I mentioned before, although it is not a hard thing to do, it can be dangerous. If you don’t feel comfortable doing it just bring in an HVAC technician to do it for you.