Air handler motor died?

oil pan 4 · 10-27-14, 01:31 AM

Today while at my future home I noticed the air conditioner blower was taking a long time to come up to speed and was buzzing a lot.
Then one time it went to start up the motor just buzzed and hardly turned over. Exactly like a 3 phase motor trying to start on 2 phases. Having all my HVAC stuff several hours drive away there was not much I could do aside from check to see that the fan spun freely which it did.
I switched the wires so that the low speed windings would be used for A/C and the same thing happened.
With out my fluke meters and milk crate full of motor capacitors I couldn't even test the capacitor or swap it to see if it was bad or test the winding for a ground fault or short circuit.

Now if the motor run capacitor was bad I figured the motor would hum and not move. This was an angry buzzing, noticeable from the other room and the motor tried to turn over some and got very hot in a very short amount of time.
I have never pulled the capacitor off one of these motors and tried to turn it on. I have a swamp cooler in my current house that has a multi speed winding motor and I think it has a motor run capacitor. If it does I will experiment on it some tomorrow. I don't have any other blowers to play with. I will check the appliance pile at the scrap yard too, I have seen a few there occasionally.

I think some of the windings are shorted.

Is there any chance its just the capacitor?
If the blower needs to be replaced are there any efficiency up grades? This install is only about 3 or 4 years old.

jeff5may · 10-27-14, 01:47 PM

my guess is that the capacitor failed shorted. In that case, the symptoms you are describing would appear. I would just swap the cap for a minute to test the motor. If the symptoms remain, you have bigger headaches ahead.

where2 · 10-27-14, 09:07 PM

I've never dissected an air handler to know whether there is a contactor inside the air handler case actually switches the alternating current based on the low voltage signal from the thermostat, or whether all that switching happens in the compressor unit. I know there is a contactor inside my A/C compressor unit. If there is a contactor involved in driving the air handler blower motor, check the contact points. I once had an issue where a small ant colony was living in my A/C compressor unit and frequently walking around the contactor. Wouldn't you know it, every so often, you'd fry one when the A/C kicked on. After I friend enough of them, I started getting a real carbon build up problem on the point surfaces, and the A/C compressor was having difficulty switching on. Fortunately, I was home and noticed the strange sound...

I polished the contact points (like cleaning the points in an old automotive distributor), and it has been working flawlessly ever since. I bought a new contactor just in case, but it's still in the cardboard box. Raid took care of the ants.

jeff5may · 10-27-14, 09:57 PM

Haha! Bugs suck, especially flying ones with stingers. We have wasps and yellow jackets here that will build a nest anywhere they can outdoors. Any time I go out to work on any stationary electrical or mechanical device, I bring a can of bug spray or brake parts cleaner. Too many bad experiences in the past.

Air handler units usually have control board with relays on them, hard wired contactors, or sequencers in them somewhere. The good news is most of them have some kind of schematic or wiring diagram in the box. Whether or not the included information is useful is another story...

MN Renovator · 10-28-14, 01:23 PM

Could be just the capacitor, I've had that happen once on the fan for an outdoor condenser and it just hummed and slowly very turned but eventually it would speed up enough to spin up to a normal speed.

Two years ago on the hottest day of July the compressor wouldn't fire up and popped the breaker. I ohmed the windings against the case and it wasn't shorted to ground and so I checked the resistance between each winding connection and everything checked out so I replaced the capacitor and once it was out I realized it was soaked in oil.

My personal checklist is: 1. Check if the motor spins freely and without bearing noise. 2. Ohm case to windings to check for a short. 3. Make sure all connections are clean and connected firmly. 4. Try another speed tap if there are others. If this is still failing, I usually remove the motor and wire power directly rather than through the appliance.

If everything checks out and it is a PSC motor, I replace the cap. If it is not a perm-lubed motor and I can oil it, I'll oil the motor.

A personal note, I once had a motor that ran fine and would eventually get hot and slow down. Turns out it was shorted to ground and I forgot to check. I pulled the blower from the cabinet and while supporting the blower housing with one hand I hit the door safety switch with the other hand and felt a surprise. Be sure to have a ground attached when playing with motors.

Standard disclaimer - Don't mess with motors or electricity unless you know how to not get injured or killed. Getting caught in fan blades, burned, etc. can result in a bad day.

oil pan 4 · 11-15-14, 01:22 AM

I went back a week or 2 later and tested the capacitor, it had capacitance, the correct amount, I do not know. But they usually fail open.
The windings had continuity. Its a multi speed motor so I tried sticking the low speed A/C power wire on the heater relay output and it did the same thing.
It has pretty low continuity to ground so I think some of the windings are shorted.
The blower spins freely.
I did not bring my test plugin cord to hot wire the motor.

oil pan 4 · 12-20-14, 07:39 PM

Well I replaced that blower motor my self, the capacitor run coils had much higher than resistance through them.
The capacitor was fine, I reused it. It is a 7.5uf 370 volt capacitor, it tests as being 8uf on my fluke325 meter.

oil pan 4 · 01-03-15, 03:49 AM

I replaced what could have been a $600 4 speed motor with a much cheaper 3 speed motor. So far it works flawlessly in heater mode.

It appears that 2 of the 4 speeds served no purpose.
Heat runs the high speed windings only.
A/C appears to only run one of the lower speed windings.

Moral of the story:
Don't waste hundreds of dollars on a hard to find, single source 4 speed blower motor when a 3 speed will do the exact same job for several hundred dollars less.

NiHaoMike · 01-03-15, 10:32 AM

You could have just got a single speed motor that will be even cheaper and more efficient, especially when your climate requires little or no dehumidification.

oil pan 4 · 01-03-15, 11:25 AM

I thought about that, but this house is in a part of texas that has 100% humidity pretty much all summer.
I have a feeling that the fan high speed setting could blow water off the coils and all over the in side of the ducting.
Then blowing the air over the evap coils at full speed would increase the heat load on the compressor and I don't know if it could take it on the hottest days.

10-27-14, 01:31 AM	#1
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	Air handler motor died? Today while at my future home I noticed the air conditioner blower was taking a long time to come up to speed and was buzzing a lot. Then one time it went to start up the motor just buzzed and hardly turned over. Exactly like a 3 phase motor trying to start on 2 phases. Having all my HVAC stuff several hours drive away there was not much I could do aside from check to see that the fan spun freely which it did. I switched the wires so that the low speed windings would be used for A/C and the same thing happened. With out my fluke meters and milk crate full of motor capacitors I couldn't even test the capacitor or swap it to see if it was bad or test the winding for a ground fault or short circuit. Now if the motor run capacitor was bad I figured the motor would hum and not move. This was an angry buzzing, noticeable from the other room and the motor tried to turn over some and got very hot in a very short amount of time. I have never pulled the capacitor off one of these motors and tried to turn it on. I have a swamp cooler in my current house that has a multi speed winding motor and I think it has a motor run capacitor. If it does I will experiment on it some tomorrow. I don't have any other blowers to play with. I will check the appliance pile at the scrap yard too, I have seen a few there occasionally. I think some of the windings are shorted. Is there any chance its just the capacitor? If the blower needs to be replaced are there any efficiency up grades? This install is only about 3 or 4 years old. Last edited by oil pan 4; 10-27-14 at 01:36 AM..

10-28-14, 01:23 PM	#5
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 939 Thanks: 41 Thanked 116 Times in 90 Posts	Could be just the capacitor, I've had that happen once on the fan for an outdoor condenser and it just hummed and slowly very turned but eventually it would speed up enough to spin up to a normal speed. Two years ago on the hottest day of July the compressor wouldn't fire up and popped the breaker. I ohmed the windings against the case and it wasn't shorted to ground and so I checked the resistance between each winding connection and everything checked out so I replaced the capacitor and once it was out I realized it was soaked in oil. My personal checklist is: 1. Check if the motor spins freely and without bearing noise. 2. Ohm case to windings to check for a short. 3. Make sure all connections are clean and connected firmly. 4. Try another speed tap if there are others. If this is still failing, I usually remove the motor and wire power directly rather than through the appliance. If everything checks out and it is a PSC motor, I replace the cap. If it is not a perm-lubed motor and I can oil it, I'll oil the motor. A personal note, I once had a motor that ran fine and would eventually get hot and slow down. Turns out it was shorted to ground and I forgot to check. I pulled the blower from the cabinet and while supporting the blower housing with one hand I hit the door safety switch with the other hand and felt a surprise. Be sure to have a ground attached when playing with motors. Standard disclaimer - Don't mess with motors or electricity unless you know how to not get injured or killed. Getting caught in fan blades, burned, etc. can result in a bad day. Last edited by MN Renovator; 10-28-14 at 01:27 PM..

01-03-15, 10:32 AM	#9
NiHaoMike Supreme EcoRenovator Join Date: Oct 2008 Location: Austin, TX Posts: 1,154 Thanks: 14 Thanked 257 Times in 241 Posts	You could have just got a single speed motor that will be even cheaper and more efficient, especially when your climate requires little or no dehumidification. __________________ To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...

10-27-14, 01:47 PM	#2
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	my guess is that the capacitor failed shorted. In that case, the symptoms you are describing would appear. I would just swap the cap for a minute to test the motor. If the symptoms remain, you have bigger headaches ahead.

10-27-14, 09:07 PM	#3
where2 DIY Geek Join Date: Apr 2013 Location: Sunny Florida Posts: 401 Thanks: 74 Thanked 83 Times in 73 Posts	I've never dissected an air handler to know whether there is a contactor inside the air handler case actually switches the alternating current based on the low voltage signal from the thermostat, or whether all that switching happens in the compressor unit. I know there is a contactor inside my A/C compressor unit. If there is a contactor involved in driving the air handler blower motor, check the contact points. I once had an issue where a small ant colony was living in my A/C compressor unit and frequently walking around the contactor. Wouldn't you know it, every so often, you'd fry one when the A/C kicked on. After I friend enough of them, I started getting a real carbon build up problem on the point surfaces, and the A/C compressor was having difficulty switching on. Fortunately, I was home and noticed the strange sound... I polished the contact points (like cleaning the points in an old automotive distributor), and it has been working flawlessly ever since. I bought a new contactor just in case, but it's still in the cardboard box. Raid took care of the ants.

10-27-14, 09:57 PM	#4
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Haha! Bugs suck, especially flying ones with stingers. We have wasps and yellow jackets here that will build a nest anywhere they can outdoors. Any time I go out to work on any stationary electrical or mechanical device, I bring a can of bug spray or brake parts cleaner. Too many bad experiences in the past. Air handler units usually have control board with relays on them, hard wired contactors, or sequencers in them somewhere. The good news is most of them have some kind of schematic or wiring diagram in the box. Whether or not the included information is useful is another story...

11-15-14, 01:22 AM	#6
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	I went back a week or 2 later and tested the capacitor, it had capacitance, the correct amount, I do not know. But they usually fail open. The windings had continuity. Its a multi speed motor so I tried sticking the low speed A/C power wire on the heater relay output and it did the same thing. It has pretty low continuity to ground so I think some of the windings are shorted. The blower spins freely. I did not bring my test plugin cord to hot wire the motor.

12-20-14, 07:39 PM	#7
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	Well I replaced that blower motor my self, the capacitor run coils had much higher than resistance through them. The capacitor was fine, I reused it. It is a 7.5uf 370 volt capacitor, it tests as being 8uf on my fluke325 meter.

01-03-15, 03:49 AM	#8
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	I replaced what could have been a $600 4 speed motor with a much cheaper 3 speed motor. So far it works flawlessly in heater mode. It appears that 2 of the 4 speeds served no purpose. Heat runs the high speed windings only. A/C appears to only run one of the lower speed windings. Moral of the story: Don't waste hundreds of dollars on a hard to find, single source 4 speed blower motor when a 3 speed will do the exact same job for several hundred dollars less.

01-03-15, 11:25 AM	#10
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	I thought about that, but this house is in a part of texas that has 100% humidity pretty much all summer. I have a feeling that the fan high speed setting could blow water off the coils and all over the in side of the ducting. Then blowing the air over the evap coils at full speed would increase the heat load on the compressor and I don't know if it could take it on the hottest days.