What’s the difference between a start capacitor & a run capacitor?

Imagine getting ready to do a load of laundry, but your washing machine won’t start. Or maybe your refrigerator isn’t cooling properly. These problems often traces back to a small but crucial component: the capacitor. Understanding the difference between a start capacitor and a run capacitor can help you troubleshoot and get your appliances working again. Let’s explore how these capacitors keep your household devices running smoothly.

Understanding capacitors in household appliances

Capacitors are essential in appliances with electric motors, such as washing machines, dryers, and refrigerators. They store and release electrical energy, providing the extra power needed to start the motor and keep it running efficiently.

The role of capacitors

Think of a capacitor like a fast-charging battery. In appliances, capacitors help overcome the initial resistance when starting a motor and then support its operation. Without them, motors might struggle to start or run inconsistently.

What is a start capacitor?

A start capacitor delivers a large electrical boost to start a motor. It temporarily increases torque, enabling the motor to overcome initial resistance and start spinning.

• How it works: When the appliance is switched on, the start capacitor releases a burst of energy that creates a phase shift in the motor’s windings, generating the extra torque needed to start the motor. Once the motor reaches a set speed, the start capacitor disconnects from the circuit.
• Applications: Start capacitors are commonly used in appliances that require high starting torque, such as air conditioners, refrigerators, and some washing machines and dryers.

What is a run capacitor?

A run capacitor stays in the circuit continuously while the motor is running, maintaining a steady voltage to ensure smooth and efficient operation.

• How it works: A run capacitor provides a constant phase shift, helping the motor run smoothly by balancing the current in the windings. This improves energy efficiency and motor performance.
• Applications: Run capacitors are typically found in appliances that need continuous, efficient operation, such as refrigerators, air conditioners, and gas dryers.

Key differences between start and run capacitors

• Functionality: Start capacitors provide a temporary boost to start the motor, whereas run capacitors maintain smooth motor operation.
• Time in circuit: Start capacitors are connected only during startup, while run capacitors remain in the circuit the entire time the motor runs.
• Capacitance values: Start capacitors have higher capacitance (70-120 microfarads or more), while run capacitors have lower values (3-70 microfarads).
• Physical characteristics: Start capacitors are typically larger and often encased in plastic, while run capacitors are smaller and may have a metal casing for heat dissipation.
• Voltage ratings: Start capacitors are designed for short, high-voltage bursts, while run capacitors are rated for continuous operation.

Signs of a faulty capacitor

Symptoms of a bad capacitor include:

• The motor won’t start
• The appliance hums but doesn’t run
• Slow or intermittent starts
• Overheating motor

Safety tips

• Always handle capacitors carefully to avoid electric shock. Capacitors can hold a charge even after the appliance is unplugged, so always discharge them before handling.
• Wear insulated gloves and safety glasses while working with capacitors to protect yourself from accidental shocks and flying debris.
• Work in a well-lit area with a stable surface to reduce the risk of accidents.
• Use only tools with insulated handles when working on electrical components.
• Refer to your appliance’s manual if you are unsure of any steps or specifications.
• If you are uncomfortable or inexperienced with electrical repairs, seek professional help. Safety should always be your top priority.
• Ensure the appliance is completely unplugged before starting any work, and double-check the power is off before proceeding.

How to test a capacitor using a multimeter

You can test a capacitor at home with a multimeter. Make sure the appliance is unplugged and the capacitor is discharged to avoid shock.

• Step-by-step guide:
  1. Locate the capacitor: Refer to the appliance manual to locate the capacitor. It is typically found near the motor or compressor.
  2. Discharge the capacitor: Use an insulated screwdriver, a resistor, or a capacitor discharge tool to safely discharge the capacitor. This step is crucial to avoid electric shock.
  3. Remove the capacitor: Carefully disconnect the wires attached to the capacitor terminals. Make sure to take note of the wiring configuration or take a picture for easy reference when reconnecting.
  4. Set your multimeter: Set your multimeter to the capacitance setting, usually marked with an ‘F’ symbol.
  5. Measure the capacitance: Place the multimeter probes on the capacitor terminals. Ensure you have a good connection. The multimeter will display a reading, which you should compare to the capacitance value printed on the side of the capacitor.
  6. Interpret the results: If the measured value is close to the rated capacitance, the capacitor is good. If the value is significantly lower, or if the multimeter displays an open or short circuit, the capacitor needs replacement.

Replacing a faulty capacitor

Tools you need: Screwdrivers, pliers, an insulated screwdriver or discharge tool, and a replacement capacitor with matching specifications.

Step-by-step replacement guide:

1. Buy the correct capacitor: Purchase a capacitor that matches the old one in both capacitance and voltage ratings. These specifications are usually printed on the side of the capacitor.
2. Prepare the appliance: Unplug the appliance and ensure it is safe to work on. Discharge the old capacitor using an insulated screwdriver, a resistor, or a capacitor discharge tool.
3. Remove the old capacitor: Disconnect the wires from the capacitor terminals, noting or photographing their positions for easy reinstallation. Unscrew or unclip the capacitor from its mounting.
4. Install the new capacitor: Position the new capacitor in place and secure it with any mounting brackets or screws. Reconnect the wires to the correct terminals based on your notes or the reference photo.
5. Reassemble the appliance: Once the new capacitor is installed, reassemble any panels or covers you removed to access the capacitor.
6. Test the appliance: Plug in the appliance and turn it on to verify that it operates properly. The motor should start smoothly, and the appliance should run without any humming or hesitation.

Additional information

Thanks for reading! If you need replacement parts, grab your model number and head to AppliancePartsPros.com. We offer over two million parts and most orders arrive in two business days. If you need help finding the right part or placing an order, you can contact our team at 1 (877) 477-7278.

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