Hot Air Furnace Problem

several but in over 90% of cases the motor you used as a replacement is capable of dunning at more than a single speed, did you wire the common wire and the "high speed wire" to your electrical leads?

The only thing I did was to switch the red and black, thinking the rotation was backward. I didn't see any instructions on the lable for other speeds, but I'll look and get back to you tonight. It really does feel like it isn't going fast enough. When the other blower came on, the ducts would collapse and make a loud gong. I long for that sound again.

generally "black is high speed, "red is medium" and yellow or white is common but its never completely standardized color coding, did you get a wiring diagram on or in the box??

Is the fan blades on backwards?

its most likely a squirrel cage and he cant put it on backwards and still get to the set screw.........it only really fits one way.

Have you confirmed the whereabouts of the plumber? He isn't inside the vent (thus preventing the longed-for 'gong' sound), is he?

What is the motor supply voltage supposed to be? I would not think it to be 220VAC, but might be, I guess.

No blockages in the ducts. The fan is indeed a squirrel cage. I took channel locks on one end of the shaft and tried to turn the other end, so there is no slippage. I think Fredski has the answer and that there is a way to wire it for more RPMs. I just don't know how. I didn't check the voltage, but I don't think it's 220. This is a very standard burner and fan.

"This is a very standard burner and fan."

Standard for what? I am assuming your house, but we don't really know.. Neither do we know where you are... perhaps you have motor intended for 60hz and the power supply is 50hz.

I know you think you're giving us a lot of information, but we don't have much to go on, except the plumber isn't stuck in a duct and the furnace doesn't blow very much air.

notice I learned my lesson and haven't once mentioned seeking out a professional...

He hired a professional who ripped the motor appart...

Maybe the same guy?

Now that's a great picture!!! Maybe we should start a thread where everyone posts their "Oops, does the NEC cover that?" pictures or stories.

sorry, this isn't NEMA rating and the prints specifically called for NEMA!!!

I would check any capacitors involved(make sure they are good and proper size for that motor), proper wiring(make sure the motor is proper voltage requirement and everything is wired correctly), blower wheel orientation and integrity(sometimes they slip on the hub)....check motor amp draw, bearing could be binding....the amp draw will tell the tale....Usually blower fans will operate on a lower speed for heat(med or low) and sometimes when a speed is lost rather than change out the motor it is just wired for high speed in both cooling and heating....if this was the case and the fan is now operating on low speed instead of the improvised high speed, then the fan may be operating properly....

thats one of them new high efficiency jobs

There are forward curved blades and backward curved blades, depending on the application....this application should be a forward curved blade(the anim)....the backward curved blades are for higher pressure medium flow applications, while the forward curved blades are for high volume low pressure applications....Having the proper orientation of the fan blades is necessary for success here.....but seeing that the OP doesn't even know the voltage here, I think this information may be superfluous....

correction; ".this application should be a forward curved blade(the anim)"....is in fact not the animation which is backward curved blades....however the application here would typically call for a forward curved blade blower wheel, and CW rotation...

Forward curved centrifugal fan blades are directionally sensitive. The motor is probably turning in the wrong direction. Changing a single wire will not change the rotational direction of a single phase AC induction motor. The leads to either the "start" winding or the "run" winding must be reversed to do this.

The owner should take advantage of the disassembled condition of his air handler to clean those forward curved blades. Forward curved blades experience dust buildup, which will also reduce his airflow.

Have you checked the plumber's work to make sure he didn't leave anything in the ducts? Depending what it might have been, it could be lodged somewhere that it is not obvious to you. Did he change the settings on any dampers in the return ducts? Closed ones could reduce the available amount of air. Are there any dampers that were left open on the discharge ducts? This would lower the air pressure in the ducts and prevent the air from going where you want it to go. Are there any access panels on the exhaust (hot air) ducts that might have been left off? This would also let the air escape. Is the set screw that locks the cage to the shaft tight? Have you checked the mechanical functions of the complete system? Not all problems are electrical.

Not to discredit any plumbers or pipefitters but they are not perfect, just as everyone else is not perfect. Some are not as perfect as others.

Good Luck, Old Salt

I found a jacket in the ducts of my house one time. I was furious at the electrician, until I discovered it was mine....

Well, the house was cold.

And it was hard to work in a jacket.

And the floor was muddy.

So I found a place to stash it for "just a few minutes".

Yes! I won't mention any of mine though, there isn't enough space here. What is good about them is they are usually a very good learning experience.

Years ago when I took my first class in firefighting, they were teaching us how to make forcible entry of doors. With this class, no matter where it is taken, the first question the instructors ask is what is the first thing you do when forcing entry through a door. The answer is obvious but few get it right--> "Try the knob, it may not be locked!"

We live and learn.

Good Luck, Old Salt

Did he apply aluminum tape to all the joints?

Excellent example. GA

Good Luck, Old Salt

Ohm the motor leads. The one with most resistance is low speed wire. Circuit board on furnace will have a high speed slot marked. Amp the motor as well. If you have an ECM motor on furnace then you don't get the bang in duct work and it's a different type of air movement people aren't used to.also check static pressure it should not be more than 0.05. If blower is moving to slow then the Safety switch will open due to over heating of heat exchanger

wouldn't it be faster just to look at the diagram on the motor and leave the meter in your tool bag?

it may not have a circuit board, it may simply be switched in the thermostat sub base

Most of you all seem to be thinking in terms of Home or building HVAC blower. I think the OP is in an industrial setting with an actual "HOT AIR FURNACE". (sorry caps, but I did want emphasize). Some of these applications if not most will have 3 phase 460 V motor on the blower, and wire sense is key. OP has not apparently done all his homework, or the cat ate it. Centrifugal switch, uh oh, maybe this is a 110 V motor.

(1) verify motor speed by nameplate comparisons, yes.

(2) check nameplates on motors for correct voltage, amps, HP, phases, etc.

(3) make sure the air path is not blocked (as stated by others).

(4) find the actual manual supplied with the original blower system and read it.

I somewhat doubt he had a plumber out to a plant to work on his industrial furnace but it is possible. but as usual light information leads to assumptions

It is not apparent from the original post that this is an Industrial furnace. From the post I was assuming it was a residential application.

A residential application would likely be a 110/220 VAC motor, which can come in 2 speeds and direction of rotation is usually plainly marked on the name plate data.

However, an accidential partial blockage may have occurred. There is not enough information to trouble shoot the system from a computer, we can only make guesses according to our experience.

thanks, Bob, and Fredski. Yes, I wish he had used a different terminology than "hot air furnace". The term "home central heating and cooling blower" comes to mind. Or "blower to home furnace". Or make and model number....

James,

I believe that most of us were thinking correctly, after all he did say a "...plumber ripped it apart...", I would have expected "maintenance personnel" would do that in an industrial setting. And yes, a centrifugal switch is not something we find in (m)any 3 phase industrial motor applications.

Alan

Sorry for not clarifying all the minutiae. It is a home heating system. For a 1600 square foot home. With the old blower motor, the house would warm from 60 to 70 in 20 minutes. Now it takes an hour and a half. The air coming from the ducts blew hard enough to swing curtains back and forth. With the new motor, same ratings as the old motor, 110VAC, 1/3 HP, 1750 RPMs, there is half the volume of air moving. The furnace does shut off occasionally for overheating. I don't know how any duct could be blocked since THE ONLY THING THAT CHANGED WAS THE MOTOR!!!!!

here's a typical universal replacement blower motor. you'll notice white, blue, red wire. these offer different speeds of the same HP rating, so red motor might spec as 1750RPM but Thats just ON THE HIGHEST SPEED. you have choices on actual speed. you also have direction considerations.

OK, I am totally busted. Just do not replace one of these during a cold snap like I had to over the holidays (and yes on a weekend). $946.00 later we are back off the fireplace. I could have done myself even buying at a high dollar place like Grainger.

My opinion: many ways to get this wrong, only one way it goes in right. Cell phones also take wonderful pictures these days.

Have you checked the rotation? (Switching the wires will not change the rotation just the speed).

The forward curved squirrel cage type fans will still move a little bit of air even if they are turning backwards.

Check the rotation of the motor and make sure it is correct.

Check the fan orientation and make sure it was not intsalled backwards.

Thank you VERY much for coming back to us with your solution. So many don't!