In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term still encountered in a few compound names, such as the condenser microphone. It is a passive electronic component with two terminals.
The utility of a capacitor depends on its capacitance. While some capacitance exists between any two electrical conductors in proximity in a circuit, a capacitor is a component designed specifically to add capacitance to some part of the circuit.
The physical form and construction of practical capacitors vary widely and many types of capacitor are in common use. Most capacitors contain at least two electrical conductors, often in the form of metallic plates or surfaces separated by a dielectric medium. A conductor may be a foil, thin film, sintered bead of metal, or an electrolyte. The nonconducting dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, mica, air, and oxide layers. When an electric potential difference (a voltage) is applied across the terminals of a capacitor, for example when a capacitor is connected across a battery, an electric field develops across the dielectric, causing a net positive charge to collect on one plate and net negative charge to collect on the other plate. No current actually flows through a perfect dielectric. However, there is a flow of charge through the source circuit. If the condition is maintained sufficiently long, the current through the source circuit ceases. If a time-varying voltage is applied across the leads of the capacitor, the source experiences an ongoing current due to the charging and discharging cycles of the capacitor.
Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy, although real-life capacitors do dissipate a small amount (see Non-ideal behavior).
The earliest forms of capacitors were created in the 1740s, when European experimenters discovered that electric charge could be stored in water-filled glass jars that came to be known as Leyden jars. Today, capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. In analog filter networks, they smooth the output of power supplies. In resonant circuits they tune radios to particular frequencies. In electric power transmission systems, they stabilize voltage and power flow. The property of energy storage in capacitors was exploited as dynamic memory in early digital computers and still is in modern DRAM.
To test an AC capacitor, you’ll need to purchase a multimeter, a tool used to test the voltage, current, and resistance in electrical devices. A multimeter is a small handheld device equipped with a dial, two probes, and a digital display.
These devices aren’t expensive and are available at most home improvement stores. Make sure you purchase one that allows you to test the capacitance, which is the ability to store an electric charge.
Since you’ll be working with an appliance that uses high voltage, be sure to take the proper precautions to minimize the risk of electric shock. Do not start working on the air conditioning unit until you’ve cut off power to it at the breaker. It’s a good idea to use a non-contact voltage tester to verify there is no electricity running through the unit; you can buy one at your local home improvement store for about $10.
Even after you’ve cut power to the AC unit, the capacitor will still hold a charge that’s powerful enough to hurt you. Carefully follow the instructions below to discharge it safely.
Follow the steps below to test the capacitor on your air conditioning unit. Since you’ll be working with an electrical appliance, make sure you follow each step carefully to minimize the risk of electric shock.
1.Cut Off the Power
Locate the breaker on your home’s electrical panel and cut the power to the AC unit to ensure no electricity is flowing through it while you’re testing the AC capacitor. A central AC unit will be on one of the panel’s 230-volt breakers.
2. Locate the Capacitor
Using a screwdriver, remove the access panel on your air conditioning unit. The capacitor should be easy to spot. It’s silver, cylindrical, about the size of a soda can, and has wires of various colors connected to it.
3. Release the Charge
Since a capacitor stores an electric charge, you’ll need to release that energy before you can safely work on it to eliminate the risk of shock. Use the metal end of your screwdriver to connect the capacitor’s electrical terminals to each other to release the charge.
Make sure you use a screwdriver with a plastic or rubber-insulated handle and don’t allow your hands to come into contact with any exposed metal on the screwdriver while you’re releasing the charge in the capacitor.
4. Remove the Capacitor
Now that you’ve discharged the capacitor, you can safely remove it from the AC unit. Begin by taking a picture of the wiring, so you can reinstall the capacitor after testing or replacing it. Next, unplug each of the wires connected to the capacitor, then unscrew the brackets holding the capacitor to the air conditioner and pull it out.
5. Check Its Condition
Before testing the capacitor, visually examine it. When a capacitor fails, it often bulges or leaks. If your AC’s capacitor has either symptom, you’ll need to replace it.
6. Identify the Capacitor’s Rating
You’ll need to know what you’re looking for before you can test your capacitor. Check the capacitor’s label for its microfarad (MFD) rating, which is a measurement of the amount of electricity the capacitor can store.
If you’re testing a single capacitor, you’ll find a single microfarad rating on the label. Dual capacitors have two microfarad ratings; the higher rating is for the compressor while the lower rating is for the fan motor.
Next to the microfarad ratings, you’ll also see a percentage on the label with a plus and minus sign. This percentage tells you how far off the listed microfarad ratings the capacitor can be and still function properly. For example, a capacitor with a rating of 25 microfarads and a plus or minus rating of 5% will have readings between 23.75 and 26.25 microfarads on the micrometer if it’s functioning normally.
7. Set Up the Multimeter
Turn the dial on the multimeter to the setting for capacitance. Most multimeters use the symbol –|(– to signify capacity. You should also see a uF symbol on the display, which stands for microfarads. If you’re not sure which setting on the dial to use, consult the multimeter's instructions for how to find the setting for testing capacitance. After you have the multimeter dialed in, plug the two probes into the meter’s outlets.
8. Test the Capacitor
How you test the capacitor varies depending on whether you have a single capacitor, which only has two terminals, or a dual capacitor, which has three terminals.
1) Testing a Single Capacitor
Place the first probe on one of the multimeter’s terminals and the second probe on the other terminal, then check the meter’s digital display. Compare the reading to the rating on the label to see if it's functioning normally. Don’t forget to account for the margin of error percentage.
2) Testing a Dual Capacitor
A dual capacitor provides a power boost for both the fan and the compressor and has three terminals. One terminal will be labeled “C” for common terminal, another labeled “FAN” for the air conditioner fan motor, and a third labeled either “HERM” or “COMP” for the unit’s hermetic compressor.
Start by testing the fan terminal by connecting one probe to the common terminal and one to the fan terminal. Next, test the hermetic compressor by placing one probe on the common terminal and the other on the hermetic compressor’s terminal.
Again, compare the readings to the rating on the label to see if the capacitor is functioning normally. If either the rating for the fan or compressor is off by more than the percentage listed on the capacitor label, you’ll need to replace the capacitor.
Type CBB65 Capacitors (including round, oval, single and dual) are used in motor run, HVAC/R, UPS, refrigerator and other general purpose applications, are designed for continuous operation and are energized the entire time the motor is running.
35uf 5uf 370-440V Dual Run Capacitor CBB65 AC Electric Motor Start HVAC Blower Compressor Furnace 35MFD / 5MFD / CBB65-R
General Features:
AC capacitors usually last from 10 to 20 years, depending on the size, type and quality. However, if you don’t service your AC unit regularly, it can greatly reduce the lifespan of your capacitor. Additionally, if you choose the wrong voltage for your unit or your capacitor experiences prolonged exposure to high heat, it’s not likely to last as long.
There are several signs that your AC capacitor might be broken, including:
Since AC capacitors are high-voltage components that might cause significant injury to you even if the power is out. This is why we advise our clients not to open their unit's door to install a new capacitor without a help of a professional. It is strongly recommended against changing them yourself.