Furnace is super loudówould like to turn my fan speed down?


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Old 04-02-19, 11:48 AM
J
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Question Furnace is super loudówould like to turn my fan speed down?

Hi all,

New member here—excited to be a part of the community!

I have an older furnace and I'm hoping to figure out how to turn the speed of the blower/fan motor down. The fan itself isn't loud, and it's not like whistling or anything, it's just that it blows super fast and the air, like... rushes, loudly, out of my vents. It's more than capable of blowing papers off the table and pushes a ton of hot air up your pants/skirt/etc if you happen to be standing over a vent, and the sound of rushing air can be really loud and annoying. I'm sure this is intentional—it's an older house with floor registers and so pumping air all throughout the house is probably the most efficient way to heat things. However, I'm willing to take the efficiency hit in order to run my blower at a more reasonable speed. I think the furnace just blows too fast for the house... I live in a pretty small house, and the fan goes really fast.

I watched some youtube videos and it looks like most of them just kind of let you run different wires to change the fan speed, but I don't see any loose wires in my furnace.

It's a "Model N8MPL075B12A1 ICP FURNACE/HEATER", and I found the manual on the sears parts direct website, so maybe it's made by sears? I also took a picture of the fan area circuit board:

and just general layout of the fan area:

It also has an area where the actual flame kicks on, which is separate from the fan box:

Please let me know if any other photos would be helpful. Really hoping to figure out how to get this fan slowed down (ideally slowed down a whole lot)! Don't see an manufacturer or any wiring diagrams anywhere in there. Would super appreciate even a starting point on where to look or things to test. I'm pretty good with tools and generally pretty good with wiring, but I can't seem to crack this particular nut.

Thank you in advance for any guidance! Please let me know if there is any other information I should provide.

Have a good one, everybody! thanks!
 

Last edited by PJmax; 04-02-19 at 06:04 PM. Reason: removed non working links
  #2  
Old 04-02-19, 11:59 AM
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All your photo links failed, so no pics.
 
  #3  
Old 04-02-19, 12:01 PM
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I can't open the photos. Change the asterisks to the original characters.

If your fan has a multi-speed motor, its speed can be changed by changing the electrical connections. Otherwise, probably not.
 
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Old 04-02-19, 12:55 PM
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You have to check the temperature rise before and after changing the fan speed.

Read how here: https://structuretech1.com/diy-furnace-test/

Adjusting the blower speed without measurements to confirm it's correct can cause damage.

Too high and the heat exchanger overheats and eventually cracks.

Too low you can you get condensation in the heat exchanger leading to corrosion and failure.

Most furnaces have the blower factory set to deliver proper airflow on a decent duct system. Having excessive noise is an indication that the ducts are already undersized (and or furnace oversized) and cutting the speed below factory will overheat the furnace.

Your unit has a standard blower motor with 4 speeds, usually one is used for cooling, one heat and the others are on park terminals. Some circuit boards may use a separate speed for continuous fan, I doubt yours does due to being a lower end brand.

You change the speed by moving the wires around on the board.

Connect the desired speed to the heating blower terminal and the unused one on park.

The schematic shows the wiring and should tell you which wire color corresponds with which speed.

But again, proceed with caution, don't just change it without measurements.
 
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Old 04-02-19, 01:38 PM
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Sorry for the inconvenience... I'll try to upload them in a post....

picture of the fan area circuit board:
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just general layout of the fan area:
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It also has an area where the actual flame kicks on, which is separate from the fan box:
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Last edited by PJmax; 04-02-19 at 08:59 PM. Reason: resized pictures
  #6  
Old 04-02-19, 01:44 PM
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The blower speed connections are on the bottom left. I can't tell which speeds are connected, too many wires in the way.

Post a clear pic of schematic, it should be on the blower access panel side facing into the unit.

I can tell you it's a heat only system and they never bothered to connect a wire to control continuous fan from the thermostat. After dealing with this, I recommend looking into that, you can run the fan and circulate air in the summer, particularly useful if the house is 2-story.

Do you have a thermometer you can insert into the duct?
 

Last edited by user 10; 04-02-19 at 03:38 PM.
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Old 04-02-19, 08:13 PM
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You were using a picture host that DIY does not allow. That's what the x's were.

Blue and red are parked. Black is on cool terminal. Leaves orange on heat terminal.
The speeds are: black = high, blue = medium, orange = medium low, red = low.

I don't think you can go much lower. Furnaces are rarely run on slow speed.

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M1 & M2 are parked wires.
 

Last edited by PJmax; 04-02-19 at 09:01 PM.
  #8  
Old 04-03-19, 06:16 PM
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Yes - Normally medium high or medium low is used for heat on single stage units like yours.

Low is only there for continuous fan or 1.5 ton a/c.
 
 

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