Furnace Not Blowing Hard

diyordie · 08-06-2010, 11:11 AM

I just moved into a new home this summer. The furnace is old but the air cond. is just 2 years old. The air blows cold but it barely trickles out of the vents. With such low volume of air blowing, the air cond. runs constantly and can't get the temperature down.

I pull the access panel off while the blower is running and it is spinning freely but not very fast. It is a belt drive and the belt appears to be in good condition.

I suspect the blower motor is on it's way out but I don't know much about them. Would a motor that is failing not be able to get up to speed or would it simply stop working? Can a faulty run capacitor cause this or is it most likely the motor itself?

Thanks in advance for any help.

oberkc · 08-06-2010, 12:57 PM

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

diyordie · 08-06-2010, 01:19 PM

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

diyordie · 08-06-2010, 01:46 PM

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.

**beenthere** · 08-06-2010, 11:17 PM

Is the belt tight?

Red Squirrel · 08-06-2010, 11:44 PM

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.

williswires · 08-07-2010, 11:23 PM

What is the "blower" are you talking about?

bobelectric · 08-08-2010, 05:59 AM

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

diyordie · 08-08-2010, 08:36 PM

@ 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

yuri · 08-08-2010, 09:05 PM

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.

**beenthere** · 08-08-2010, 10:06 PM

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.

lloydb · 08-08-2010, 11:20 PM

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.

bobelectric · 08-09-2010, 05:17 AM

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

diyordie · 08-09-2010, 07:35 AM

@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.

rjniles · 08-09-2010, 07:54 AM

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.