How to Test Start Capacitors on Furnace Blowers

Testing the start capacitor on a furnace is essential to ensure efficient and reliable operation of the blower motor. Here's how you can test the start capacitor on a furnace blower:

1. Safety Precautions:

- Before starting any electrical work, ensure the power supply to the furnace is turned off.

- Use appropriate safety gear, such as insulated tools, gloves, and safety glasses.

2. Preparation:

- Locate the start capacitor in the furnace. It is usually cylindrical or box-shaped and connected to the blower motor.

- Remove any covers or access panels to expose the capacitor's terminals.

3. Identification:

- Take note of the capacitor's specifications printed on its body, including its capacitance (measured in microfarads) and voltage rating.

4. Disconnect Capacitor:

- Carefully discharge the capacitor by shorting its terminals with an insulated screwdriver. This is necessary to avoid any stored energy in the capacitor.

5. Multimeter Measurement:

- Set your multimeter to the capacitance measurement range.

- Connect the positive (red) probe of the multimeter to the "C" terminal of the capacitor, and the negative (black) probe to the common terminal (usually marked with a "C" or "COM").

6. Capacitor Test:

- If the multimeter displays a reading close to the capacitance specified on the capacitor, it indicates that the capacitor is functioning properly.

7. Additional Troubleshooting:

- If the multimeter display a reading significantly lower than expected or indicates "OL" (over limit), the capacitor may be faulty and needs to be replaced.

- If the capacitance reading is higher than expected, the capacitor may have deteriorated but is still functional. However, it's recommended to replace it for long-term reliability.

- If the multimeter displays a reading of "0" (zero) or "1", the capacitor is potentially shorted and needs to be replaced immediately.

8. Capacitor Replacement:

- If the capacitor needs to be replaced, purchase a new capacitor with the same or slightly higher capacitance and voltage rating as the original capacitor.

- Disconnect the power supply and discharge the capacitor before replacing it.

- Follow the manufacturer's instructions to install the new capacitor.

9. Test the Furnace Blower:

- Once the capacitor is replaced, turn on the power supply and check if the furnace blower operates smoothly.

10. Safety First:

- Always follow safety guidelines and best electrical practices when performing any maintenance on the furnace. If you're not comfortable handling electrical components, consider seeking professional assistance.

Remember, testing start capacitors involves working with electrical components. If you are unsure about any step, it's recommended to consult a professional technician to ensure safe and proper handling.