I have an old Carrier natural gas furnace (model number is 58SSB) which makes a lot of noise in the past several years. At the beginning, I thought it is the issue of blower motor. Every time when furnace is starting to work, I can feel a vibration even on the first floor. At that time I didn't have lot of knowledge about gas furnace, and had no ideas about the differences of blower motor and inducer motor. Until recently, I got chance to trouble-shoot the problem.
When I started to open the Carrier furnace, I already knew that the issue is on the draft inducer. Most likely the noises and vibration are caused by a damaged inducer motor or unbalanced wheel, I thought at that time.
What is draft inducer in a furnace?
The inducer assembly is a fan to pull warm air through the furnace heat exchanger and send it to outside(chimney) through a vent pipe. The draft inducer is designed specifically to ensure combustion gas is properly vented out of your furnace, and heat is distributed evenly throughout the walls of heat exchanger, and provide the burners with a constant source of oxygen. The draft inducer starts up 30-60 seconds before the burners are lit and continues to run until burners are off. Draft inducers are monitored by an air pressure switch. If the pressure switch detects that there is an inadequate amount of air blowing through the heat exchanger, or if there is no air blowing at all, the system will be shut down.
The trouble-shooting process
To remove draft inducer motor from housing is not difficult. First unplug power wire from inducer control board, then remove 4 mounting bolts (not the 3 bigger mounting grommets), the motor and blower wheel will be easily taken out from blower housing. Visually check the motor, motor fan, and blower wheel to see any damages, unbalance, or worn, but I found nothing. I clamped the motor on tabletop for a quick test with 115 volt current. Both motor and wheel run smoothly without vibration and noises.
After closer look, I found the cause of vibration is the worn motor mounting grommets (Model#: KA56GR540).
To order these mounting grommets will take some time. I pulled them out and swapped their positions. Does the temporary fix work? The result is positive.
How much does it cost?
The cost to purchase a new draft inducer motor including blower wheel is $200.
Cost of inducer motor only is about $50.
Cost of blower wheel is $35.
Cost of mounting grommet is $10 each.
Part number list
Inducer motor: HC23UZ120
Motor mounting grommet: KA56GR540
Blower wheel: LA11AA004
Inducer control board kit: 58SX306620-705