How to Troubleshoot a Furnace Motor
Motors are a common failure for heating and cooling systems. They fail either due to age or improper maintenance. A properly maintained motor will provide years of trouble free operation.
SO HOW DO YOU KNOW IF YOUR MOTOR HAS FAILED OR IS ABOUT TO FAIL?
- During routine maintenance checks HVAC technicians will monitor the amperage load to the motor. A high amperage will indicate the motor is working too hard and is going to fail in the near future. The easiest way to check the amperage is with an amp meter on the common wire to the motor. Most motors use multiple speeds and each speed has its own specific wire. Using the common wire for an amperage reading takes out the guess work
- When you turn on your system no air comes out of the vents and you have already checked for a dirty filter and clogged evaporator coil.
- The motor makes a humming sound and does not start.
- The motor starts and runs for a short period of time and shuts off again. This is due to the motor overheating and shutting off on thermal overload. HVAC motors have thermal overloads to shut the motor off when it becomes too hot. The easiest way to check this is to manually check the motor using your hand. BE EXTREMELY CAREFUL WHEN DOING THIS! A hot motor can and will burn you. If you are checking an indoor blower motor, be sure to disconnect the power prior to checking. Place your hand close to the motor without touching it and sense the heat. If it is too hot to touch, then the blower motor is overheating and it is time to replace it. An outdoor condenser motor can be check by feeling the grill it is attached to without taking the cover off. If the motor is attached in another fashion then follow proper safety to check.
- The air coming out of the vents has a hot electrical burning smell to it. An overheated motor is one of many parts that will omit a smell when is failing. Turn the power off! The hot electrical smell can be noticed on condenser motors just by standing over the unit when is running.
- The motor starting is making a louder than usual noise and it is slow to come up to speed.
- A motor can be started manually be spinning the fan or blower wheel. USE CAUTION WHEN DOING THIS AS INJURY CAN RESULT. Use an object such as a wood stick to start the fan or blower wheel. If it is hard to spin, then the motor has failed.
- Verify the run capacitor for the proper rating.
This guide's intention is to provide an understanding of the operation of a furnace. It is not intended as a hands-on teaching tool, or aide. All HVAC equipment should be serviced by a licensed HVAC technician. Consult your local, town, city, and state laws, ordinances, and regulations prior to accessing, engaging, troubleshooting, repairing, or servicing any HVAC equipment.
SAFETY NOTE - ALWAYS TURN THE MAIN POWER AND GAS VALVE OFF BEFORE SERVICING ANY HVAC EQUIPMENT. SERIOUS INJURY CAN OCCUR.