The start capacitor for one model of a Bostitch air compressor is shown below. To see if your capacitor is within specification set the meter to the capacitance mode and apply the test leads to the terminals – it will take a few seconds as the meter is actually charging the capacitor and then reading it in farads. If you have any questions regarding how to test capacitors on air compressor motors then please leave a comment below with a photo if applicable so that someone can help you!
Replacing the start capacitor can generally be divided into three steps: removing the start capacitor, finding a replaceable start capacitor, and replacing the start capacitor. After removing the damaged compressor start capacitor, then select a suitable new start capacitor to replace it according to the specifications and volume of the damaged start capacitor. The run voltage of the start capacitor is greater than or equal to 1.42 U. The working capacitor is 1-4UF per 100W, and the start capacitor is 4-10 times the working capacitor.
This article gives a description of electric motor capacitor test procedures to determine if a capacitor is damaged or working normally & test procedures to measure the capacitor’s capacitance or microfarads, MFD, or uF to determine if it is working within its rated capacitance range. This article series gives electric motor start-run capacitor and hard-start capacitor installation instructions to get a hard-starting air conditioner compressor motor, fan motor, refrigerator, or freezer compressor or other electric motor going. Discussed here: description of electric motor capacitor test procedures to determine if a capacitor is damaged or working normally & test procedures to measure the capacitor’s capacitance or microfarads, MFD, or uF to determine if it is working within its rated capacitance range.
The start capacitor cover on your compressor motor may look the same as the one shown in the photo, or might differ slightly. If the compressor motor start capacitor has failed, the power supply to the motor stops there, and the motor will not start. If you’ve checked the capacitor and it’s good, then possibly the electric motor itself has failed, particularly if, when you power up the air compressor with the tank empty, and power flowing to the tested start capacitor, your compressor motor makes no sound at all.
A single run capacitor supports a single electric motor and is commonly used in small air conditioners and microwave ovens; a dual run capacitor will support two motors, the first being a compressor and the second being a fan motor. How to tell if a capacitor is bad. Over time, a run capacitor can weaken and lose its ability to hold a full charge. You will need to use a dedicated capacitor tester for this test or a multimeter that has a capacitor testing function.
To see if your capacitor is within specification set the meter to the capacitance mode and apply the test leads to the terminals – it will take a few seconds as the meter is actually charging the capacitor and then reading it in farads. The purpose of the start capacitor is to help the compressor get going. The run capacitor is placed in series with the start winding of the compressor and will remain in the circuit as the motor operates.
how to test air compressor start capacitor Related Question:
How do you identify a starting capacitor and a running capacitor?
The voltage classifications are 370V and 440V. Capacitors with ratings above 70 microfarad (uF) are starting capacitors. Run capacitors are designed for continuous duty, and are energized the entire time the motor is running. Single phase electric motors need a capacitor to energize a second phase winding.
How do you tell if a capacitor is bad with a multimeter?
Use the multimeter and read the voltage on the capacitor leads. The voltage should read near 9 volts. The voltage will discharge rapidly to 0V because the capacitor is discharging through the multimeter. If the capacitor will not retain that voltage, it is defective and should be replaced.
What happens when start capacitor goes bad?
If a run capacitor fails, the motor can display a variety of problems including not starting, overheating, and vibrating. A bad run capacitor deprives the motor of the full voltage it needs to operate correctly.
How many ohms should a capacitor have?
A normal capacitor would have a resistance reading up somewhere in between these 2 extremes, say, anywhere in the tens of thousands or hundreds of thousands of ohms. But not 0Ω or several MΩ. This is a simple but effective method for finding out if a capacitor is defective or not.
Will compressor run if capacitor is bad?
The most common problem that bad capacitors can cause is “hard starting.” This is when the compressor of an AC has difficulty starting up, stutters trying to turn on, and then shuts off a short while later.
What causes a start capacitor to fail?
Overheating is a primary cause of a failed start capacitor. Start capacitors are not designed to dissipate the heat associated with continuous operation; they are designed to stay in the circuit only momentarily while the motor is starting. If a start capacitor stays in the circuit too long, it will overheat and fail.
What would be the symptoms of an open start capacitor on a capacitor start motor?
A capacitor that is open-circuited will show no current movement when tested across its terminals with an ohmmeter. In most cases, motors with open capacitors won’t start at all. Short-circuited capacitors will show zero resistance when measured with an ohmmeter.
How do you check a motor start capacitor?
To spot a dual run capacitor that operates both the compressor and the fan motor, look for three terminals on the capacitor: one will be marked “common” or may be marked with a red dot to indicate that role.
Can I use a run capacitor in place of a start capacitor?
The capacitance and voltage ratings would have to match the original start capacitor specification. A start capacitor can never be used as a run capacitor, because it cannot not handle current continuously.
Should capacitor have continuity?
Capacitors should not have continuity. However, when testing the capacitor using the continuity function of a multimeter you might get intermittent ‘beeping’ due to the capacitor charging and discharging.
How do you charge a capacitor with a multimeter?
Place the voltmeter positive node on the positive terminals of the capacitor and the negative node on the ground terminal of the capacitor and set the meter to Volts DC. Once the volt meter reads 11 or 12 volts you can remove the voltmeter and replace the resistor with the power fuse.
What is the capacitor symbol on a multimeter?
To measure capacitance, you will need to plug your leads into the correct ports on your multimeter. Your red lead goes into the port marked with the “–|(–” symbol. This is the symbol for capacitance. Your black lead will be plugged into the port marked with “COM”.
What does OL mean when testing a capacitor?
An “OL” or “overload” reading means the capacitance is too high for the multimeter to measure. Set the multimeter to a higher range if possible. This result can also mean the capacitor has shorted. An auto-ranging multimeter will test the lowest range first, then increase if it hits an overload.
How do you test a start capacitor with an ohm meter?
To test the capacitor with a multimeter, set the meter to read in the high ohms range, somewhere above 10k and 1m ohms. Touch the meter leads to the corresponding leads on the capacitor, red to positive and black to negative. The meter should start at zero and then moving slowly toward infinity.
