A Knocking Noise in a Trane Furnace Heat Pump

The Noises

• Listen carefully to the loud noise the next time the heat pump is automatically activated and the furnace begins a cycle. If the noise resembles a loud “thunk” or a thud, chances are the pump’s compressor is starting to fail. In this case, shut off the main power to the furnace system and call a repair person: this type of repair lies outside the parameters of the average person’s know-how, so turn off the system to preserve the compressor and call in a licensed technician.

The Blower

• Check the blower on the furnace system by manually spinning the blades on the fan. This do-it-yourself approach should be taken should the furnace be making a loud screech or scratching noise as opposed to a dull thud. Chances are components on the blower are rubbing against one another and making the noise, so add a few drops of lubricant oil to the ports. If it still doesn’t spin, the motor is to blame and needs to be replaced.

Motor Removal

• Disconnect the wires leading to the blower and use an adjustable wrench to loosen the blower’s holding bolts – generally speaking there are only two or three of them, and once they’re free you can easily pull out the blower assembly. Remove the screws that anchor the wheel to the motor then remove the holding bolts; the motor should now be free from the assembly so pull it out and note the model information printed somewhere on its surface. Take the information to a dealer and purchase a new motor for the unit.

And Motor Replacement

• Line up the center of the wheel to the new housing cover on the motor. Make sure the wheel rotates in the right direction; installing the wheel to spin in the wrong direction means having to backtrack and repeat your work. Should any wires be left unused, a common occurrence when using a modern motor with older model systems, fold a strip of electrical tape over the exposed ends for safety reasons.

Check Your Work

• Reverse the steps you did when you removed the assembly to finish replacing the motor. Turn on the system again to a heat setting that causes the blower to engage. If it comes on, you’re done; if not, the capacitor may need to be replaced, which is yet another job for a repairman.