How to Test HVAC Capacitors

How to Test HVAC Capacitors

Capacitors are essential components of the HVAC system. The motors, including the compressor, would not function without them. 

It is a simple device that stores a large amount of energy. Many high energy applications, including your HVAC system, now employ capacitors.

Although HVAC is linked to your home’s electric cables, it is insufficient to activate it when you want cold air. The capacitor balances the shortfall, ensuring that your HVAC has enough energy to complete the job. 

What Is a Capacitor?

A capacitor is a sort of charge-holding electrical device. It is present in HVAC systems on fan motors and compressors. They have two different electrical ratings. 

The first rating is the capacitance of the unit, which is in microfarads (mfd). The device can store the charge quantity when a specific voltage is applied. 

The second is a voltage rating, which specifies the supply voltage for the item. This is usually 370 or 440 volts in HVAC systems. It is critical because the capacitor will fail prematurely if a considerably larger voltage is supplied.

Types of Capacitors in HVAC

Capacitors used in HVAC systems are of two categories:

Run Capacitor

These capacitors are in furnaces, air conditioners, and heat pumps. In addition, these capacitors are present in fan motors and compressors. They provide motors with a reasonably steady voltage and enhance their torque during startup.

Start Capacitor

They are present in some air conditioners and heat pumps. They offer additional power to the compressor when it starts. After the compressor runs, a potential sensor immediately disables them from the compressor.

HVAC Capacitor Testing

Below are some steps that you should follow to test an HVAC Capacitor.

Disconnect the Power

First, disconnect the power to the unit at the breaker panel outside the home near the condensing unit.

Locating and Examining the Capacitor

After disconnecting the power, disconnect the service panel from the unit.

Find the start capacitor. It’s probably silver, round or oval and has several prongs on top for wiring.

Examine the surface of the capacitor where prongs are present and consider if it appears high or curved.

When a capacitor blows, the top of the capacitor will be pushed up or swelled, similar to a popped can that is dropped and is ready to burst.

This form of a capacitor is one of the apparent signs of being damaged.

Discharging the Capacitor’s Power

You’ve already turned off the HVAC unit; now it’s time to discharge the capacitor’s charge.

As previously stated, a capacitor stores energy. So it’s possible that the capacitor is still powered up and ready to shoot. 

Tapping the terminals with your palm simultaneously will release this power, resulting in a frightening sensation.

Also, before continuing, discharge your capacitor by crossing the terminals with an insulated-handle screwdriver.

Taking Down the Old Capacitor

Double check the place for any electrical current where you will be working using the circuit alert device. Now you can remove the old capacitor. 

A metal band most likely attaches the capacitor with one screw to the device. When you remove that screw, the capacitor should pop out of the unit.

Also, make a drawing or label showing which wire goes where before removing the wires from the old capacitor.

Connecting the New Capacitor

You may remove the wires with simple needle pliers once you’ve identified where they’ll connect to the new capacitor. 

Also, if the wires are too tight to yank, utilize a rocking motion while slowly tugging on them. It will prevent you from accidentally touching another terminal or having the pliers slide and strike you. 

And you are done. All you have to do now is find the correct replacement component and replace it the same way you removed the old one.

How Can You Visually Test an HVAC Capacitor?

Before testing, you can visually check the capacitor. If the capacitor exhibits one of the following visual indicators, it is damaged:

  • The capacitor’s dielectric fluid is pouring out.
  • The capacitor’s top cap is dripping with grease.
  • There is a rapid growth of the capacitor’s top cap.
  • The capacitor’s body appears to be enlarging.

HVAC Capacitor Testing with a Multimeter

A multimeter is a device that measures electric current, voltage, and, in most cases, the resistance across a wide range of values.

A multimeter is necessary for capacitor testing. A capacitance setting is available on several digital meters. The capacitor’s two terminals are combined using a screwdriver after turning off the power source. 

The unit will discharge this way, and you will not receive any electric shock. 

Next, disconnect the cables from the capacitor. Finally, the meter’s leads are connected to the terminals, and you can take a reading. 

Also, you should obtain the reading within 6% of the capacitor’s rated capacity. 

Change the capacitor if the reading is 6% lower than the rating. If you have an analog meter, you may check the capacitor by setting the meter to measure resistance.

Now turn off the power, discharge the capacitor, and unplug the capacitor’s cables. Place the wires on the capacitor terminals. Set the meter to the highest resistance level. 

The resistance reading should begin at zero and increase until it reaches its maximum value. 

Protruding the unit or an oily liquid seeping from it are two evident symptoms that the capacitor is faulty.

HVAC Capacitor Testing with Analog Meter

Follow these instructions to examine a capacitor using an AVO (Ampere, Volt, Ohm Meter) in the Resistance or Ohm mode.

  • Check to see if the capacitor has completely discharged.
  • Take a look at an AVO meter.
  • Select the analog meter’s resistance “OHM” mode by rotating the knob. Always select the higher range of Ohms.
  • Connect the capacitor connections to the meter leads (COM to the “-ve” terminals, Positive to the “+ve”).
  • Take note of the reading and compare it to the findings below.
  • Capacitors with a short lifespan: The resistance of a shorted capacitor will be meager.
  • Open Capacitors: On the OHM meter, an available capacitor will not exhibit any movement.
  • Capacitors that work well will have little resistance at first, then steadily rise to the infinite. It indicates that the capacitor is in perfect working order.


Although you can’t stop a power failure from destroying your capacitor. You can have regular HVAC maintenance to ensure that your system is in good working order.

Staying cautious with your HVAC system will help you extend its life and ensure that it isn’t consuming too much of your energy budget.

Warwick Braith

Warwick Braith is a thrill seeker at heart. He loves getting outdoors and testing his limits in the wild. As a blogger for YapQ, Warwick provides readers with insights and tips on how to get the most out of their outdoor experiences. Whether it's hiking, camping, or simply exploring nature, Warwick knows how to make the most of it.

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