How to Test HVAC Capacitor and How to Fix It

HVAC (heating, ventilation, and air conditioning) systems are critical to maintaining acceptable interior temperatures in both residential and commercial buildings. The capacitor is an important component of an HVAC system because it stores and releases electrical energy to operate the compressor, fan motor, and blower motor.

A malfunctioning capacitor may cause your HVAC system to fail, resulting in increased energy costs, lower interior comfort, and even equipment damage. 

In this article, we'll go over how to test an HVAC capacitor and how to repair it if it's broken.

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What is a capacitor?

A component of an HVAC system that stores and then releases electrical energy is called a capacitor. Capacitors are commonly installed in the motors of the compressor and the fan to provide an initial surge of electrical energy to start the motor and to maintain the motor's smooth operation.

A malfunctioning capacitor may cause an HVAC system to malfunction, which can result in higher energy costs, a reduction in the level of comfort experienced within the building, and possible damage to the equipment. Capacitors are vital to the reliable operation of an HVAC system.

Testing the Capacitor

To prevent electric shock, switch off the electricity to the HVAC system before testing the capacitor. A multimeter, a screwdriver, and pliers are also required.

1: Locate the capacitor

A capacitor is usually a cylindrical or oval-shaped component with two or three terminals. The rating of the capacitor is shown on its body, which also indicates its capacitance and voltage rating. You may also look up the capacitor and its placement in the HVAC system's handbook.

2: Discharge the capacitor

Even when the power is turned off, capacitors retain electrical energy. You must discharge the capacitor before testing it to avoid electric shock. You may short the capacitor's terminals using a screwdriver with an insulated handle by pressing the screwdriver's metal end to each terminal at the same time. This will discharge the electrical charge in the capacitor.

3: Determine the capacitance of the capacitor

Set your multimeter to measure capacitance - some have special settings to do so. Next, contact the multimeter probes to the capacitor's terminals, making sure that they are touching the correct terminals. The capacitance value of the capacitor should be shown by the multimeter, and it should be within 10% of the specific capacitance. If the capacitor has a rating of 20 microfarads (μF), the measured value should be between 18 and 22 μF.

If the measured value is much less than the specified capacitance, the capacitor is weak and may not give enough energy to start the motor in the HVAC system. If the measured value exceeds the rated capacitance, the capacitor may be shorted or have a partial short, causing the HVAC system's motor to overheat and fail.

4: Check the voltage of the capacitor.

Set your multimeter to measure voltage to test the capacitor's voltage. Touch the multimeter probes to the capacitor's terminals, making sure they are in contact with the relevant terminals. The multimeter should show the capacitor's voltage rating, which should be within 10% of the stated voltage. If the capacitor is rated at 370 volts (V), the measured voltage should be between 333 and 407 V.

If the measured voltage is much lower than the rated voltage, the capacitor may not be sufficient to power the HVAC system's motor. If the measured voltage exceeds the rated value, the capacitor may be overcharged, causing the HVAC system's motor to overheat and fail.

Doing repairs to the capacitor

If the capacitance or voltage of the capacitor is outside of the allowed range, it must be replaced. A replacement capacitor with the same capacitance and voltage rating, a screwdriver, and a set of pliers are required to replace the capacitor.

1: Turn Off the Power

To avoid electric shock, turn off the electricity to the HVAC system at the breaker box or disconnect switch.

2: Unplug the capacitor

Using pliers, locate the capacitor and remove the wires from the terminals. Some capacitors are fastened to a bracket or clip that may be removed with a screwdriver.

3: Put in the new capacitor

Put the new capacitor in the same place as the old one, making sure that the terminals are in the same position. With pliers, connect the wires to the respective terminals. Refer to the HVAC system's handbook for the right wiring schematic if the replacement capacitor has three terminals.

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