# Furnace blower only runs VERY slow...



## kenmac

did you check cap with cap tester or just ohm meter ? A cap tester tells what the cap is putting out


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## tippet

I used an ohm meter for that test, with the capacitor disconnected from the motor, the number went from 0 to max over a period of about 30-45 seconds. I don't own a capacitor tester, so is there some other way to measure the output?


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## tippet

An update: Decided to replace the capacitor, just in case that was it (without being able to properly test it, thanks kenmac) - however, no change. I decided to get a better look at the motor, to see what a replacement would cost for that, so I pulled it halfway out. The blower is on top of the furnace (updraft?). Anyway, I wanted to see what would happen when I turned it on, and lo and behold the fan shot up to full speed - sounded great, didn't get hot or anything. Thinking I had somehow fixed it (a loose wire maybe), I pushed it back over the opening for the furnace and _it slowed down!_ Confused now, I pulled it back out and it sped back up. I tilted it up, to expose the bottom to open air, and it slowed down again! So apparently, the fan speeds up when it encounters a lack of airflow (when sitting on the floor, for example), then slows down when it gets plenty of air.

I assume this is a design choice, and not an accident (ie, nothing is actually broken). However, is there some way to bypass this feature and just run the fan on the speeds I want it to run?? It does little to no good operating the way it does! 

The motor is an Emerson Rescue 5461, set up to operate at 1/2 HP (10 microfarad capacitor). It appears stock in every way, and is wired into the system in what seems to be the usual manner. 

Please help!


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## beenthere

Is the motor on the other furnace also a 1/2 HP? Or is it more?

The speeding up when not moving air is an inherent feature of the design of a PSC motor. It is not bypassable.

Has it always been this way, or just recently?


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## tippet

I haven't taken apart the motor on the other furnace yet (since it works), but I can tell from what little of it that I can see that it is not the same motor - the capacitor is older, and longer, but has no label, and the motor is obviously older (has an OEM look to it, at least on the back). I can't tell what HP it has! 

I'm not entirely sure how long the furnace has been this way, we only noticed it once the weather turned cold, as we hardly ever had it pushing AC over the summer and we moved in during the spring. One thing that is interesting is that I can decrease the horsepower rating of the motor by using lower rated capacitors (all the way down to 1/6 HP) - would decreasing the HP help it run faster when there isn't enough pressure in the system?


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## beenthere

No, it wouldn't. Good chance that its not big enough(too low of a horse power) already.

Look at the label of the furnace. It may have a blower horse power rating on it. See what it says.


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## tippet

An update - we solved the motor problem, but exposed a new problem! Turns out whoever installed the motor put in a 208-230 volt model in a furnace that runs 115 volts. Once we put in a new motor, it runs like a dream, if a little wobbly and rattly.

The new problem: all of this started because no air was coming out of the vents. Now that the fan is finally up to speed, no air is coming out of the vents. So essentially I have solved nothing! Can a simple dirty coil block that much air flow? Or is it more likely that the ducts are blocked off somehow?


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## beenthere

A dirty coil can stop all air flow. See it a lot.


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## Know It ALL

Don't know if you have them Tippet but, indoor pets wreak havoc on coils.


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## yuri

Are you sure you got the rotation on the new motor correct. Let it come to a slow stop and look at the blades. Should be scooping the air. If running backwards there are 2 wires on the motor to switch.


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## tippet

Yuri wins! When we installed the new motor, I matched the rotation direction to the fan that we removed (the 230 volt fan) - this was apparently a mistake. I guess the HVAC tech who installed that fan was having an off day. Once I reversed the wires, it worked just fine. Now, the coil _is_ pretty dirty, the filters do need changed, and I am willing to bet the ducts are pretty stuffed up too, but it finally was able to get the room up to 70F without tripping the limit, and it is nice and quiet as well.

Thank you everyone! This probably saved me a lot of money...


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## beenthere

Your return ducts may be pretty dirty, But your supply probably isn't, the A/C coil keeps the supply pretty clean.


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## tbl1968

Belated thank you's! I've been fighting with my furnace for three months after replacing the blower motor. Had a local HVAC guy come out to check my freon levels and we noticed that the motor was making a noise like it was going out. He offered to the motor for $1400 and told me I wouldn't be able to buy one to do it myself. Given that this guy showed up without his tools and that I've replaced these before for about $100, I decided to do it myself. Unfortunately, after I hooked it all back up, it would only run at one speed. For the past few months, I've tried off and on to troubleshoot it and was on the verge of just having the whole furnace replaced when I ran across this article, which I had also read several weeks ago, but discounted the note about about changing the rotation, because I had set it to be the same rotation as my last motor. So on a last ditch effort before replacing the whole furnace, I switched the rotation, and presto... works like a champ. So glad I found this, and wish I had tried that earlier...it was a hot hot end of summer and a cold start of winter!


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