HVAC system, intermittent power problem.


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Old 01-30-16, 10:20 PM
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HVAC system, intermittent power problem.

Hello everyone,
I hope everyone is doing well. I found this site while searching for clues as to what might be a problem I'm having and figured I'd try posting.

My parents have recently had their HVAC blower motor blow (I was there staring at it when it happened cause it started making a noise first, blew with a nice big spark and quite a bit of smoke). Trying to help them out since money is tight for them right now, I got a matching replacement motor from a local hvac shop (new motor), and went and installed it for them tonight.

I wired everything back up the same as the old motor. It's a 220 volt, 1/2 horsepower, 3.9 amp motor. I don't know if wire colors are consistent so based on the wiring diagram I'll try to describe how it's wired. The white "line" wire, goes to an orange wire coming from the hvac panel box. I'm assuming this is an always live 110 volt line, as one video I saw said it was neutral in a 110 volt system. Then, I wired the black wire from the panel to the black wire on the blower. Near as I can figure, this line is 110volt hot when the ac is running to have the motor run on hi. Then a blue wire from the panel to the red wire on the blower. I'm guessing this wire is 110 volt hot when the heater is running, and red makes the motor run on low. The ground was connected to the squirrel cage, and the yellow blue from the motor were not wired to anything. Like I said, I matched these up and wired as the old motor was.

Anyway, once wired I flipped the fan on the thermostat over to on instead of auto to test it, turned the breaker on, and it made one heck of a racket. Upon closer inspection to me it seems as if the motor is not getting constant power. It kicks on and off repeatedly and causes a racket. As soon as I cut power to it, the fan continues to spin freely and silently for a little while and I don't see any wobble in it.

I tried a few different wiring situations to see if anything helped but it did not. So then, I decided to actually make the AC come on and see what would happen. I had my Mom open the backdoor which put the outside AC unit in view and let me be able to hear it. As soon as I flipped the breaker to allow the unit to cut on, the fan on the unit outside was doing the same exact thing as the blower motor, and in perfect timing with it. It also caused all the lights in the house to dim at this point.

This is about the extent of my know how, I dabble in electronics as a hobby, but nothing on this scale usually, so I only know the basics. I don't know if this is signs of a short somewhere, a bad blower motor causing some kind of problem, or if one of the things in the hvac panel could possible be damaged causing this behavior. One of the breakers on the hvac panel was tripped after the motor blew, so I suppose it's possible that something else in there got damaged. I don't see any signs of any scorching on anything though to indicate any arcing. The only piece I can readily identify in that box is a relay lol.

I didn't see any lose connections on anything, and I triple checked all the stuff I wired was making solid connections. I don't really think a loose connection would be the culprit here, otherwise it should've been happening to the old blower motor before it blew (it was not, the old one was apparently it's to big for their current heating system, according to a hvac professional).

So, I know this information is somewhat vague, but hoping maybe it's enough that someone can point me in the right direction to go from here. I'm still hoping I can do something to keep my parents from having to spend a lot of money to get a professional hvac serviceman out there to fix this. The last time they were out there they told my parents about the problem with the blower being to big for the heating system (apparently because it was upgraded when the ac system got upgraded last year), they said it would cost them 1500 dollars to fix it fully. I'm just trying to help get them by for now until they can afford to have a pro come out and take care of everything else that needs to be done.

Thanks for any advice!
 
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Old 01-30-16, 10:32 PM
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Welcome to the forums.

It's almost impossible to follow your wiring connections.
If you're working with a 240v motor there should not be 120v there.

Post the make and model of the furnace/air handler.

Pictures also help us to see what you are seeing. http://www.doityourself.com/forum/el...-pictures.html
 

Last edited by PJmax; 01-30-16 at 10:53 PM.
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Old 01-31-16, 08:55 AM
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As for the 240v vs 120v, 240v consists of two 120v legs of power, afaik. I've never seen 240v running down a single line of power, at least not in an american wring system.

I added the wiring information as best I could just to describe the situation. I'm hoping maybe someone can diagnosis a possible problem location based on the symptoms, more so than the wiring connections. I'll try to get my Mom to go back there and take a couple of pictures, they live about an hour away from me so not sure when I'll get back over to take pictures.

EDIT:
Ok here are some pictures I just had my mom take. I don't know for sure if the model is correct on this label. I know the motor information is not the same on it. They upgraded the motor last year in the summer to a 1/2 HP 3.9amp motor when they upgraded the AC system.

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Last edited by steven6282; 01-31-16 at 09:20 AM.
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Old 01-31-16, 09:22 AM
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You didn't mention anything about a capacitor for the motor.
Do you know which motor you used ? A link maybe ?

Since you're working with 240v to the blower motor.... I'm guessing this is a heat pump system and not a furnace.

A make and model lets me know what you are working on. There should be an ID tag on the outside of the unit. There should also be a wiring diagram on the back of the blower door.
 
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Old 01-31-16, 10:17 AM
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Oh sorry, I thought capacitors were standard on these. Every motor I looked at when looking at replacments had one. No id tags on the outside of the unit, no labels on the back of the blower door. The only label is the one in the attached pictures, it has a model and serial number on there but I have no idea how accurate it is or what it goes to. I don't know if it's considered a heat pump or not, it's a split system with ac compressor outside and heater coils inside.

EDIT:
Oh, here is the label for the new motor.
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Like I said, this is a match to the old motor that was in the system.
 

Last edited by steven6282; 01-31-16 at 12:56 PM.
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Old 01-31-16, 02:20 PM
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To me it sounds like you have a short in your control wiring. What I think is going on is that the short is drawing too many amps from the control transformer and the voltage going to the blower fan motor drops enough to release the fan motor relay.

The reason this burned out the fan motor is because when you start the motor it draws a lot of amps and creates a lot of heat. When you are constantly starting the heat never dissipates and it burns out the motor.

Start with a visual inspection of all your control wiring going into the blower to see if you can find a bare spot that is grounding it out. You also need to ohm out any coils to see if they are shorted internally. I have had the reversing valve coil short internally causing a very similar condition. It still had continuity but the ohms were too low causing it to draw too many amps when the relay coils kicked in.

Edit: Something else to check would be your heat strip sequencers. They can fail stuck on. This causes a huge immediate amp draw which could be causing your 240 supply voltage to the transformer to drop causing a drop in your 24 volt control wiring. This would also explain why the lights dimmed. Normally your heat strips are turned on in stages to prevent huge amp spikes that overload the system.
 

Last edited by fire67bird; 01-31-16 at 02:50 PM.
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Old 01-31-16, 04:39 PM
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You have a Nordyne E2EB-015HA air handler.
The manual is here..... nortek hvac/literature/359a.pdf
Page 16 is the wiring diagram for your unit including blower motor wiring.

Based on that diagram and the new motor diagram it appears you wired it correctly.

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