Blower acting oddly


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Old 02-06-15, 02:15 PM
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Blower acting oddly

Hi All,

Hopefully someone can give me some ideas here.

The motor on my furnace was changed out and now it is behaving oddly. If I turn the blower on using the manual control, it will run fine with no load (belt off), or under low load- if a have a filter in place, but as soon as I close the filter door the motor will start turning off and on. There isn't any kind of switch that monitors the filter door, so that is not an issue. It seems like if there is too much load it keeps tripping off. I tried slowing the blower speed by opening up the V pulley and it becomes even more sensitive (won't run even with the filter in). Any thoughts? This motor is a direct replacement for the one that was taken out. The fan/limit switch is new, the bearings on the blower are new and well greased. There is good air flow at both the cold air returns and heating vents when it is run without the filter door, so there doesn't seem to be an obstruction. The voltage to the motor is constant, but I don't have an amp meter at home to measure the draw.

Thanks
 
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Old 02-06-15, 02:40 PM
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Who changed it out, and how long ago? I would be on the phone with the installer.
 
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Old 02-06-15, 02:57 PM
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That is part of the problem. I havn't been able to get a hold of the guy for the last three weeks since he changed it out.
 
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Old 02-06-15, 03:10 PM
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It could be a belt tension problem. If you squeeze the belt together 1/2 way between the pulleys, there should be about 3/4" movement before you start to move the motor.
 
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Old 02-06-15, 03:11 PM
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How long does it run before it goes off?
 
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Old 02-06-15, 03:30 PM
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Belt tension seems good-there is about 3/4" flex before the motor moves.
It comes up to what sounds like full speed, shuts off for maybe half a second, then kicks back on. Comes back up to full speed, kicks off....will keep doing this as long as I let it.
 
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Old 02-06-15, 03:53 PM
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I have to believe you have a bad motor.
 
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Old 02-08-15, 07:52 AM
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Update and new question

So, I looked a little closer at the name plate on the old and new motors-everything matched. Looked closer and noticed the catalog number was different. Went to the Marathon catalog and found out that the old motor didn't have overload protection, the new one does. (Cat. B318 vs. B319). This can't be determined from the model number! Anyway, the old motor would run for a bit of time (~15-30 sec.) and then sound like it was coming under heavy load before it made a popping noise like a relay tripping. It would immediately come back on, reach full speed in maybe 2 seconds, come under load, pop. This cycle would repeat as long as we let it. We reasoned that the bearings in the blower might be going bad and swapped out the brass for new ball bearings. Same thing happened. So, next we reasoned that the motor was the problem. Swapped for what we thought was an identical motor. Now it has the problem described below. It gets up to speed quickly and then a quiet relay (?) trips, the motor shuts off for maybe 0.5 sec. or less and then it comes back on. This will repeat as long as I let it. So, my question is, am I still seeing an overload condition, like I saw with the old motor, that causes a different/earlier protection trip? Is the problem not with the motor, but with the blower fan? It turns real easy by hand. I'm trying to get ahold of a tech at Marathon without luck, yet. If I get them to swap out the B319 for a B318 do you think that would fix it?

Thanks for all your help!
 
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Old 02-08-15, 01:18 PM
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Do you have any of the supply registers in the house closed or otherwise blocked? If you do then it is possible that you are overloading the motor by increasing the duct pressure. Check also for any balancing dampers in the ductwork that may have slipped from their original setting and are now closed.

Or, you may be overloading the motor by turning the blower too fast. If this is the case then you will need to either put a smaller pulley on the motor or if the motor has an adjustable pulley, space the pulley so the belt rides lower in the groove. A new belt may be necessary with either of these modifications.

IF you try the slower speed then you MUST also check the temperature differential across the heat exchanger to make sure it still falls between the manufacturer's recommendation.
 
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Old 02-08-15, 01:26 PM
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http://www.amazon.com/Marathon-Blowe.../dp/B00178LGTI


That capacitor start, induction run motor can be wired for 230 volts or for 115 volts.

How is your motor wired?

What is the air handler voltage listed on the nomenclature (tag).
If both voltages are listed measure your voltage.

Is the motor pulley about 2/3 the size of your blower pulley?
 

Last edited by Houston204; 02-08-15 at 02:58 PM.
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Old 02-08-15, 03:07 PM
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That is the slightly odd thing. I tried slowing the fan speed down by opening up the pulley and it makes it shut off under at base load, without any of the panels on. I'm assuming that with a "smaller" motor pulley there is an increase in load. All the supply registers are wide open and I haven't found any balancing dampers closed down. I might have one or two in the attic that I will have to crawl around to find.
 
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Old 02-08-15, 03:14 PM
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Houston,
From the wiring diagrams it looks like there is only a change for rotation direction. I can't find anything for changing between 115/230. Is there a jumper(s) I need to change?

The air handler voltage is listed at 105 and by meter it keeps 105 during operation.

The motor pulley is roughly 2/3 the size of the blower pulley (3 /4" vs. 5").

Thanks for all the suggestions guys!

I have to figure out what the expected CFM is in the blower closet and see if I'm way off.
 
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Old 02-08-15, 03:34 PM
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Strange you would mention rotattion. That's one thing we haven't addressed. Are you sure it's right?
Glad these other guys jumped in. I was starting to feel like I was grasping at straws in a hurricane.
 
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Old 02-08-15, 03:49 PM
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Yes, definitely check the rotation as that can screw you up big time.
 
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Old 02-08-15, 05:23 PM
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I think the rotation is correct

I started it up the first time and there was no flow out of the return vents. Reversed it and it feels good, so I'm pretty sure it is the correct rotation.
 
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Old 02-08-15, 07:12 PM
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The fan should rotate so the cupped blades scoop the air & sling it toward the outlet shute of the fan housing.
 
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Old 02-08-15, 09:03 PM
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I usually remove that motor when it fails and pick up a Dayton replacement from Grainger because they have it in stock but the motor tag should have a diagram much like the Dayton motors.

Post a picture of the tag on your motor that lists 1750RPM, 56 frame, 115/230 vac, 3/4 hp.

In an ideal world, the motor should come prewired for the higher voltage so that an installer doesn't smoke it.

I suspect that it is wired for 230 volts and needs to be 115 for your application.

This is an example from the Dayton motor...

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Last edited by Houston204; 02-08-15 at 09:24 PM.
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Old 02-09-15, 03:45 AM
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Sweet Mother of.....

I stared for some time at the nameplate and never made the connection in my head about the hi versus low voltage till you posted yours. I'm an idiot!!! Name:  2015-02-07 13.25.03.jpg
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A little later this morning I'll check how it is wired.

I can't say thank you enough and I'll let you know if this solves it.
 
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Old 02-09-15, 03:49 AM
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Ooops, that is the old one

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This is the new one
 
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Old 02-09-15, 04:18 AM
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Fixed!!!!

I stole down while the wife was sleeping and changed the jumpers. It was a little hard to see the brown with the motor in. Swapped 'em about and Bob's your Uncle!!!! I'll check out the temperature differential later today. It used to be running full speed, so I'll start there. Any thoughts on whether I should worry about it being a B319 instead of a B318?

Thank you so much guys!! Can't say how much it means to me having central heat again up here in the NorthEast!
 
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Old 02-09-15, 06:12 AM
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I prefer overload protection.
Your start cap may fail one day.
 
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Old 02-09-15, 08:03 AM
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Good call Houston. Very rarely do I encounter dual voltage motors on residential equipment but at 3/4 HP it should have dawned on me.
 
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Old 02-09-15, 11:24 AM
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Thanks.

I see more capacitor start / induction run motors than permanent split capacitor motors in the high rise that I spend much of my work week maintaining.

The 1.5 hp CSiR motors can have start caps that approach 1000 microfarad.
 
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Old 02-09-15, 11:42 AM
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1000 mfd, ouch. I don't want to get bit by one of those. High rise? To me anything over 3 floors is a high rise.
 
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Old 02-09-15, 12:30 PM
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The building is from 1983 and I am replacing the air handlers and the Barber Coleman 20 volt DC controls with Honeywell Prestige IAQ stats and Belimo valves.



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The P-Trap is below the camera shot.
 
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Old 02-09-15, 03:10 PM
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Heated & chilled water system? Why the copper drain? Nice looking job.
 
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Old 02-09-15, 03:21 PM
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Thanks,

The city inspector will not pass PVC drains with common return air systems.

I wrote a small excel program that allows me to calculate GPM and the btu's moved into or out of the water when 3 Pete's plugs per coil are installed and a known control valve flow coefficient is available.
 
 

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