ThermoPride Inducer issue

Old 12-12-10, 10:25 PM
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ThermoPride Inducer issue

Hello, this is my first post here, although I search here for DIY advice for all of my projects. Thanks in advance for reading.

My issue is the inducer on my thermopride MHA-75N 80% furnace. When a call for heat is made, everything behaves normally until the gas has been firing for a while (maybe 2 minutes, see video). Then, I get the 'baseball card in a bike wheel' sound, which sounds like the squirrel cage inducer is rubbing on something. This happened two years ago and I had the inducer replaced, and is now happening again. Normally, with furnace internals I would call an HVAC man pretty quick, but I don't want it to happen again in two years. I feel like I may be treating the symptom, not the problem.

I took a video of the issue, which is really just for the sound so you can hear. You can view it here: go to 2:15 to get right to the start of the noise. You can see when I push up on the bottom of it, the noise stops. I have no idea what this means.

Also, I snagged a couple of pictures to help show some issues with the inducer. One of the studs is missing to attach the housing to the unit, and also one of the studs is missing a nut. So, it is effectively held on with 2 or 3 nuts only. Additionally, there appears to be a crack in the black housing for the inducer.

Now, on to my questions: A.) Is this a DIY repair, or better left to a contractor? B.) How would one go about replacing the missing stud, as it does not appear obvious to me? C.) If I were to go DIY, I believe the housing is not the same part as the inducer, is this correct? When it was last replaced, I believe it was only the motor, not the housing that was replaced. D.) What, besides the inducer, could be the root cause of this? Two years seems awfully short for a lifespan of an inducer motor.

As for my skill level, the most complicated HVAC project I have done is to install a house humidifier last month. It is a bypass style, and I wired up an outlet to my furnace control board (thanks to Jay11J's posts).

1. In which area you live and ambient temperatures you usually experience.
St Paul, MN - Cold
2. House style and construction details.
Built in 1906, single family home
3. Make, model and age of equipment related to the problem.
ThermoPride MHA-75N, estimated 12-15 years old (not sure how to find this)
4. Fuel type.
Natural Gas
5. Water temperature and pressures of boiler systems.
6. What type of zoning do you have with your boiler system.
7. Thermostat type.
Honeywell programmable, fairly basic
7. Anything else that would be useful. No detail is to small. The more information you provide the easier it becomes for the professionals in this forum to determined the cause and correction to the problem.
Old 12-13-10, 12:18 AM
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The fact that pushing on the inducer housing causes marked variation in the noise strongly suggests the fan is rubbing on something.

Because of the rubbing, missing stud, crack and such, I'd replace the whole inducer motor assembly, which typically has the motor, fan, and any housing needed so that the whole assembly is easily bolted into the furnace.

That make R&R pretty easy, another advantage.
Old 03-25-12, 08:13 PM
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Hi IamNash, I have the exact same trouble you had with the inducer motor. I don't see any outward signs of damage, but the squirrel cage must be rubbing against the housing, as lifting it will change the noise. That noise is nerve-wracking.
What I've been trying to do is find the proper replacement blower. I've been looking online, but can't find the correct cross-reference. I have the same model too; Thermo Pride MHA-75N and it's about 12 years old. Have you found the proper replacement?
Portland, Ore
Old 03-26-12, 08:35 PM
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Sometimes the noise can be fixed easily by replacing the rubber mounting bushings. They often sag or get compressed over time. If you get real lucky, you might be able to find replacements at your local hardware or big box store. If you have to replace the whole assembly, many inducer assemblies are brand specific & you would probably have to go thru a Thermo-Pride dealer but they might sell direct to you. Here's their web site:
Thermo Pride -
Old 03-28-12, 02:10 PM
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I was able to order a replacement from Dey Distributing. I live in Saint Paul and they are the main place to buy replacement parts for all appliances in the area.

Dey Distributing - Appliance Parts Dealer

I have never asked if they ship, but I imagine they would. Cheers!

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