# Furnace Not Blowing Hard



## oberkc

Dirty filter? At least check the easy stuff first, I say.


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## diyordie

New filter, no dampers, vents open, return air vents not blocked.


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## diyordie

*Blower Motor Running Slow*

I just moved into a new house and the motor for the blower seems to be running slow. It is a belt drive blower and the belt seems to be in good shape. Would an electric motor run slow if it's ready to fail or would a faulty run capacitor cause this?

Thanks for any help.


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## beenthere

Is the belt tight?


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## Red Squirrel

Is it a multi speed blower? Maybe it's running low speed. I believe this makes it remove humidity better by keeping the system running more and cooling more slowly. I could be wrong though.


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## williswires

What is the "blower" are you talking about?


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## bobelectric

Belt drives are from the 50's .Time to upgrade to a SEER 13!


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## diyordie

@ beenthere: The belt is snug but not overly tight. It isn't new but shows no signs of cracking.

@Red Squirrel: I don't think it is a multi-speed motor. It only gives 1 rpm rating of 1725.

Here are some pics of the blower/motor and some electrical component I originally thought was the run capacitor but now I'm not so sure. Does anyone know what it is and if it could be the reason the motor doesn't seem to want to get the blower up to speed?

Oops. Sorry. The blower for the furnace. I've checked all of what I think to be obvious culprits to making the vents not blow very hard (furnace filter, dampers, vent openings, loose/bad drive belt) and everything seems okay but the blower doesn't seem to be moving very fast. The only thing I could think of is that the motor could have gone bad and won't get up to speed. I also thought it might be a bad run capacitor but I don't see one. There is some component that I can't identify I thought might be the capacitor but I'm not sure. Here are some pics. Thanks for the feedback.

@bobelectric: Agreed, furnace needs replaced and any contributions toward the $5k to replace it will be greatly appreciated


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## yuri

That is a transformer. Install a new belt as the old one could be glazed and slipping. Tighten it so that you can only press it down 1" (deflection) when pressing on the belt. For safety reasons you should get an experienced Pro to check the heat exchanger for cracks and gaskets etc and for proper combustion. CO poisoning is not a joke.


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## beenthere

Snug? How much deflectiojn?

Belts don't have to be cracked to be bad or slipping.

Check if the sheeves/pullys are shiny in the belt grooves. If so. Change the belt. A new belt is a small $ item.


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## Binkstir

Have you checked to make sure the evaporator isn't plugged? I've seen evaporators in older homes so dirty that cleaning them was like pulling a rug off a wall.


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## bobelectric

Remove belt and run motor. It may need a good oil job and grease blower bearings. Winter's Coming!


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## diyordie

@Yuri: thanks, it must be one of the old style magnetic transformers. The belt has a little less than 1" deflection. The pulleys aren't shiny and the belt doesn't appear to be slipping. I'm not ruling it out a bad belt but I really don't want to just throw parts at it hoping I find the problem. This furnace is new to me but the blower doesn't seem to be running as fast as ones I've seen.
@lloydb: I haven't checked the evaporator coil. The whole AC system is 2 years old (the house didn't have AC prior) and I didn't think that could be a problem yet. I'll give it a look but do you think that could be the reason for the blower motor to run slow?

Good idea bobelectric. I'll give that a try tonight. I don't see any oil ports on the motor. What type of grease should I use for the bearings? All I have handy is marine grease. Would a multi-meter tell me anything about if the motor is running properly? Thanks for the help.


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## rjniles

Many of those motors have multiple taps to change the motor speed. The wiring would be under that cover on the side of the motor. There should be a information decal on the motor to give you the tap change info.


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## a7ecorsair

diyordie said:


> I just moved into a new house and the motor for the blower seems to be running slow. It is a belt drive blower and the belt seems to be in good shape. Would an electric motor run slow if it's ready to fail or would a faulty run capacitor cause this?
> 
> Thanks for any help.


Why do you feel it is running slow? Furnace motors don't have to blow the curtains around in the living room when they run. Slower moving air across the heat exchanger will absorb more heat and this warm air will rise on its own when it enters the room. Make sure it is broke before you try and fix it...


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## diyordie

@a7ecorsair: I don't expect the curtains to blow around but the air coming out of the vents could barely move a feather. I'm not have a heating problem, it's a cooling issue. The AC runs for 2 days straight and the temp doesn't get under 80F (AC system about 2yrs old). The air coming out of the vents is cold. The vents themselves are very cold to the touch but the air isn't moving into the rooms with any kind of force. I haven't tried to fix anything yet. That's why I'm here trying to avoid throwing parts at it and get some help from people who know a lot more about this stuff than me.

@rjniles: I guess I assumed that the motor would already be wired properly but I'll take a look to see if it isn't wired for the higher speed setting.

Does anyone know if a motor will begin run slow if it is failing?

Thanks for all the good suggestions.


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## rjniles

You say the AC is 2 years old but obviously the furnace is much older than that. I assume it is an add-on unit with the coiling coil cut into the furnace plenum. With floor mounted duct registers a slow fan sped will move the heated air properly in the winter as hot air naturally rises. In the cooling mode the cold air wants to sink so you need to push it up from the floor with a higher fan speed. When they put in the AC they should have changed the blower speed or installed a new one if it did not have adjustable taps.

I had a system like this years ago and I added a switch on the fan motor wiring to use a slow fan speed in the winter and a higher fan speed during the cooling season. I used a standard 3 way (SPDT) wall switch.


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## a7ecorsair

Yes, cold air is harder to blow than warm air. Do you have a thermostat that has both AC and Heat? If not, how do you change over from heat to cool?
In a properly installed system, there should be a relay that switches the motor between a low speed for heat and a higher speed for cool. Since this is an add-on, a switch like suggested may be an easy way to handle this.


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## diyordie

@rjniles: Great suggestion. Yeah, it's definately an add-on. That makes a lot of sense. I think I'd prefer to have an HVAC specialist to verify that this thing is set to run at higher speeds for cooling.

@a7ecorsair: The thermostat is a newer electronic programmable model. It has a Heat/Cool switch. I'm guessing that ideally this switch should dictate the blower speed.

I haven't tried to turn the blower on the heat setting but I think I'll give it a try to see if it actually runs slower (if that's even possible).

Thanks guys. This is why I love these forums.


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## frenchelectrican

looks like you may have older single speed motor there and as few other members here did suggest few good idea as well one good way is get multi speed motor so with the heat mode it will run at the oringal speed while when in cooling mode you need to bump up the speed.

However there is very neat gotcha is when you increase the speed some case you may have to bump up from 1/3 HP to 1/2 HP motor so it will handle better at higher speed.

Merci,
Marc


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## yuri

A belt drive blower is NOT a high speed blower like a direct drive type. The different sized motor and blower pulleys are the reason. We sometimes increase the speed by putting a 3 3/4" or 4" pulley on a 1/2 hp motor on the fan but it does get loud and wheel croak your bearings soon. You should get ball/roller bearings for that fan and ideally a new furnace.:thumbsup:


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## diyordie

I watched the blower run in heat and cool modes last night and it appears to be running at the same speed. Looks like I need to call in a pro to see 1.) if the motor is bad or 2.) the thing needs re-wired to run at dual speed.

Thanks for all the help. I'll check back in and let you know how it goes.

From what I've read here and on other forums most furnaces are set up to run at low speed for heating (because hot air will rise on its own) and higher speed for cooling. Last night I watched the blower run in both heat and cool modes and there was no change in speed. Either my furnace blower was never set up for this when the new AC was installed, or the motor is failing and won't get up to the high speed. Any thoughts?


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## DexterII

On a separate, but related path, also check the crawl space or basement for any openings in the ducts, and make sure that any basement louvers are closed; you can only push so much air out of so many openings, and it is going to take the path of least resistance.


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## beenthere

Belt drive blowers are only 1 speed.


You were reading about multispeed direct drive blower motors.


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## fabrk8r

Are you sure the motor's direction of rotation is correct?

It may have been worked on before you bought the home and has been rotating the wrong direction the whole time you've lived there. A squirrel cage blower wheel will move air in the proper direction even if rotating backwards, but the volume of air moved will be about 1/2 what it would be if the rotation is correct.


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## diyordie

@beenthere: well that certainly dashed my hopes. I thought I had found the problem. Thanks for keeping me from heading in the wrong direction.

@fabrk8r: is there any way to tell if it's going the wrong the direction other than re-wiring and seeing if you get better airflow the other way? Looking at the pictures I posted earlier in this posting the squirrel cage is going clockwise.


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## beenthere

By the pictures. Looking into the blower from the perspective of pic 2. The blower wheel should be spinning counter clockwise.


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## fabrk8r

Do a thorough check for a label or stamp indicating direction of rotation.

If there is no indicator, then I would try reversing the rotation to CCW. Most blower that are designed to only move air are of the "forward curved blade" type. It appears in your pictures that the rotation may be backwards. 

If you are comfortable working with electric motors it's easy to reverse the rotation. Just make sure you shut the power off before attempting this.

You beat me beenthere! :thumbup:


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## diyordie

Well, I was just informed that a belt drive blower is generally set up to be single speed only so now I'm at a loss.


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## frenchelectrican

diyordie said:


> Well, I was just informed that a belt drive blower is generally set up to be single speed only so now I'm at a loss.


Not always the case sometime you have to look at the motour nameplate some case they will stated multi speed as well I know some belt drive motor will have mulit speed useage.

Of course the direct drive will have multi speed useage.

If you really need multi speed motour you can swap the motor and get one with higher RPM verison depending on the nameplate and use the adjustable pully to get the speed where you want it.

And some furnace they will have addtional relay to change the speed of blower as well.

Merci.
Marc


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## fabrk8r

Did you check for proper rotation as was suggested in your other thread on this subject?


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## Scuba_Dave

2 threads on same issue merged


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## diyordie

@fabrK8r: I don't recall seeing any label about direction of rotation but I'll look again. I'm pretty sure the blower was going clockwise when I looked at it last but now I'm not so sure. If it is moving clockwise I'll try re-wiring to see if it makes an improvement. Now I'm kind of glad the furnace guy I called, who is a "good friend" of my mother-in-law, didn't return my call. 

The motor only states 1725 rpm.

@frenchelectrician: I don't want to try a higher rpm motor than what is currently there for fear of damaging the bearings/belt/pulleys/etc. Is there any way to determine if the existing motor simply isn't operating at its design speed?

Please excuse the duplicate posts (HVAC and Electrical) but I wasn't sure where the problem truly was and I've recieved a lot of great feedback from both forums.

Thanks again for everyone's help.


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## frenchelectrican

diyordie said:


> @fabrK8r: I don't recall seeing any label about direction of rotation but I'll look again. I'm pretty sure the blower was going clockwise when I looked at it last but now I'm not so sure. If it is moving clockwise I'll try re-wiring to see if it makes an improvement. Now I'm kind of glad the furnace guy I called, who is a "good friend" of my mother-in-law, didn't return my call.
> 
> The motor only states 1725 rpm.
> 
> @frenchelectrician: I don't want to try a higher rpm motor than what is currently there for fear of damaging the bearings/belt/pulleys/etc. Is there any way to determine if the existing motor simply isn't operating at its design speed?
> 
> Please excuse the duplicate posts (HVAC and Electrical) but I wasn't sure where the problem truly was and I've recieved a lot of great feedback from both forums.
> 
> Thanks again for everyone's help.


Ok I can see what you mean and the motor is allready at 1725 then you can get adjustable pulley and can make it run little more faster IIRC the squrell cage blower can run little more faster but not a whole alot more without increasing the motor size that something you may have to watch on this one and one of the HVAC guys may confirm what my idea if so ., they will leave a instruction on that matter.

If you have adjustable pully then close up the gap a bit that will speed up a little more quicker but just watch the current drawage to make sure you are not excessing over what the motor nameplate stated { this item you may want to get clamp on ampmeter ask one of your freind or get one at big box store I do not know what the cost currentlly in USA due I am in France for quite a while }

Merci.
Marc


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## diyordie

fabrk8r said:


> Did you check for proper rotation as was suggested in your other thread on this subject?


Well, I haven't had a chance to check the rotation yet but I am mildly optimistic that this could be the problem. I don't know the etiquette for posting links on this forum but here goes...http://www.nyb.com/rotation-discharge.asp. This is from a company called New York Blower. They make industrial fans for stuff like dust collectors, process dryers, etc.. The diagrams seem to confirm what the rotation direction should be for a blower and if mine is running clockwise from the view shown in my pics, it is running backwards.

My major concern is that the direction specification for my motor says "Selective CCW". I'm not sure what this means. Is the motor reversible or not? Here is the specificaiton sheet for my motor I found on the manufacturer's website. http://www.marathonelectric.com/MMPS/details.jsp?item=048S17D2086
There is a link to a PDF drawing and wiring diagram on this page which indicates which leads to switch to reverse the motor but the connection diagram doesn't explicity name my motor so I want to verify that it is reversible before attempting to rewire.


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## a7ecorsair

Looking at the picture in your earlier post, I'd say the squirrel cage fan should run clockwise as viewed in the picture and that would mean the motor would run CCW as viewed from the live shaft end.


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## beenthere

There should be instructions on your motor for which wires to change to switch rotation.


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## diyordie

beenthere said:


> By the pictures. Looking into the blower from the perspective of pic 2. The blower wheel should be spinning counter clockwise.





a7ecorsair said:


> Looking at the picture in your earlier post, I'd say the squirrel cage fan should run clockwise as viewed in the picture and that would mean the motor would run CCW as viewed from the live shaft end.


I'm getting conflicting info. Who's right?


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## fabrk8r

Reverse the rotation and check the air flow. You'll know instantly if it's better. It'll take 5 minutes.

A squirrel cage running backwards produces about 25% of the air flow it should when turning the proper direction. Feel the air flow at the blower with your hand. Switch 2 wires on the motor, start it and see if you feel more air being pulled into the blower.

BTW...for safety's sake. Disconnect the power first...just sayin' (because I've heard some stories on here lately...LOL).


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## diyordie

diyordie said:


> ...http://www.nyb.com/rotation-discharge.asp. This is from a company called New York Blower. They make industrial fans for stuff like dust collectors, process dryers, etc.. The diagrams seem to confirm what the rotation direction should be for a blower and if mine is running clockwise from the view shown in my pics, it is running backwards.


I just realized my pictures from near the beginning of this thread don't really show the layout of the blower all that well. From the viewpoint of the pictures my blower looks like the "Bottom Horizontal"/"CCW" configuration shown in the New York Blower link above.


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## beenthere

Looking at the wheel from the pic you posted. The wheel should be spinning counter clock wise.
Look at the blowers in that link you posted. It shows the same thing I'm telling you.


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## fabrk8r

This is becoming a lot harder than it needs to be.


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## beenthere

fabrk8r said:


> This is becoming a lot harder than it needs to be.


ts the internet. Of course it is.


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## yuri

Wait until we get a discussion on how to determine the rotation of a oil burner pump and describe it.:laughing::yes:


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## beenthere

yuri said:


> Wait until we get a discussion on how to determine the rotation of a oil burner pump and describe it.:laughing::yes:


ROFL...

The worst and best thing they did with oil burner pumps. Is make them by rotational.

Love that black smoke that comes out of the chimney when someone doesn't check and correct the motor rotation when they swap a burner motor out.


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## frenchelectrican

beenthere said:


> ROFL...
> 
> The worst and best thing they did with oil burner pumps. Is make them by rotational.
> 
> Love that black smoke that comes out of the chimney when someone doesn't check and correct the motor rotation when they swap a burner motor out.


I have ran into like that more than once with few service calls some motor you can not able change rotation by electrically so have to swap to diffrent motor to slove the issue { just don't start with dammed DC motors they are it own world with it !!! :whistling2: }

Twice I have to change the FO pump due it was wrong rotation due they stated no fuel start.

Merci.
Marc


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## diyordie

Foiled again! I just re-checked the blower and it is indeed running counter-clockwise as it should. There must be something else causing the meager air flow. Back to the drawing board for me.


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## yuri

Measure the diameter of the pulley on the motor. Should be at least 3.75" or perhaps a 4". You need to increase its size from the basic 3.25" to overcome the resistance of the new AC coil. That furnace is a fuel guzzler and a new one would pay for it self quickly. You may need new bearings when the fan is speeded up. At 28 or more years old and with that rusty shaft it may need a new blower wheel and be difficult to take apart and expensive to repair. You should have at least a 1/3 hp and possibly a 1/2 hp motor to be able to use larger pulleys and speed it up.


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