# Furnace Troubleshooting



## Duke55 (Oct 4, 2011)

I'm new here and this is my first post. A buddy of mine was having troubles with his furnace (newer high efficient model). His furnace blower fan runs on high all the time, the heating cycle seems to work normal when calling for heat. They Replaced the board on the furnace and this did not fix the problem. The technician that came to check it out found some small voltage on the neutral (0.5V) on the power feed to the furnace. . When I went to take a look I got readings anywhere from 0.5V to 6V on the neutral, it seemed to vary with the operation of the combustion blower fan. I checked all neutral connections, and his house ground. Could not find any issues. I think that are talking about replacing his furnace, I'm just curious about this issue and it's just nagging at me... Any Ideas anyone??? I would love to hear some ideas or comments. Thanks.


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## oldtimer (Jun 10, 2010)

Duke55 said:


> I'm new here and this is my first post. A buddy of mine was having troubles with his furnace (newer high efficient model). His furnace blower fan runs on high all the time, the heating cycle seems to work normal when calling for heat. They Replaced the board on the furnace and this did not fix the problem. The technician that came to check it out found some small voltage on the neutral (0.5V) on the power feed to the furnace. . When I went to take a look I got readings anywhere from 0.5V to 6V on the neutral, it seemed to vary with the operation of the combustion blower fan. I checked all neutral connections, and his house ground. Could not find any issues. I think that are talking about replacing his furnace, I'm just curious about this issue and it's just nagging at me... Any Ideas anyone??? I would love to hear some ideas or comments. Thanks.


 The technician should have called tech support.

You are not telling us if this is an oil furnace, gas furnace or what?


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## Duke55 (Oct 4, 2011)

Oh sorry. Natural gas, three year old York high efficient, 3 stage burner, air conditioner, honeywell programable thermostat. Hmm can't think of anything else


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## Duke55 (Oct 4, 2011)

Oh I forgot his tech support was saying it was the power source, or a dirty ground. Hope that helps.


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## wildleg (Apr 12, 2009)

did you check the schematic and work your way back from the motor wiring thru the motor relays ?


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## Duke55 (Oct 4, 2011)

The only thing that I can find is on the board I'm getting 27v across all terminals except between r and y1 terminal I'm getting around 12v... The y1 terminal is for cooling. Oh and the problem is intermittent it comes and goes between 8 and 12 hrs


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## Dennis Alwon (May 9, 2009)

Has this always done this or is this new.


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## Duke55 (Oct 4, 2011)

Oh it's new, they had some power surges in the area a day before this happened. Might be related, nothing else in his house was effected.


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## Service Call (Jul 9, 2011)

Check for a bad ground / neutral at the source. If the tech said there was problem on the feed side I don't understand why you're checking the board.


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## Duke55 (Oct 4, 2011)

Checked for a bad ground and neutral back and the source (panel). I cleaned the main ground connections. I also fed the furnace from another circuit in the house, still had voltage on the neutral, then I proceeded to run a cable over to the neighbours house in order to eliminate the house completely, and still had voltage on the neutral. After that I continued to look at the furnace and the board. Only because they completely replaced the furnace on warranty within the first year already, making this the second furnace in three years, and the third board in this furnace. All this is why I'm so curious about this issue.


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## oldtimer (Jun 10, 2010)

Duke55 said:


> Checked for a bad ground and neutral back and the source (panel). I cleaned the main ground connections. I also fed the furnace from another circuit in the house, still had voltage on the neutral, then I proceeded to run a cable over to the neighbours house in order to eliminate the house completely, and still had voltage on the neutral. After that I continued to look at the furnace and the board. Only because they completely replaced the furnace on warranty within the first year already, making this the second furnace in three years, and the third board in this furnace. All this is why I'm so curious about this issue.



Just a suggestion...... talk to the neighbours. See if any one else has problems.

Also call the poco, and have them check their power.

There could be a connection that is intermittent.

I once had a similar problem, and it turned out to be in the poco drop.

It had been hit by lightning, and whenever a load (like a motor) was applied, strange things happened.

Poco changed the loop, and problem was solved.


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## RGH (Sep 12, 2011)

I dont think I would be worried about a small amount of voltage on nuetral that is probably feed back through motor winding.


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## RGH (Sep 12, 2011)

A 2 speed motor would need relay(s) to trip to call for speed/increase/decrease probably tripped by plenum heat indicator sensor. Lightning would/could fry them puppies. check for bad relay good luck pcb swap didnt work..relays next step good luck!


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## Duke55 (Oct 4, 2011)

Thanks Old Timer, I never thought about going back past the panel to the drop. I'm surprised that it wouldn't effect other stuff in the house. But I guess if that furnace is very sensitive it could be the only thing acting up. As far as the neighbours I'll tell him to ask. I was also thinking about the motor windings only because when I loaded or slowed down the combustion air motor the voltage readings on the neutral jumped all over the place. By the way thanks to everyone for their input this is great. I don't deal with this too much, I mostly work in industrial, so I'm worried that I'm missing something here.


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## lefleuron (May 22, 2010)

I hate programmable thermostats.

The worst has to be the BRYANT EVOLUTION, damn thing has a mind of its own, and an awful lot of hidden menus throughout.

I imagine someone has removed the possibility that the thermostat is doing this.


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## Duke55 (Oct 4, 2011)

Thanks RGH


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## Big John (May 23, 2010)

I agree with RGH: God knows what kind of electronic controls are in this thing, but a multispeed motor still has basic relays. Check those. I also think the "dirty ground" is techno BS for "I can't find the problem." Unless there's some serious voodoo with their circuitry I would expect that furnace to run fine even if completely ungrounded.

Something is calling for high fan speed and pulling in a contact somewhere. Find out what.

-John


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## Duke55 (Oct 4, 2011)

I asked the tech about the thermostat and they said it was good. I wanted to try another one, but they weren't interested in swapping it out. I could see the thermostat being responsible for the erratic behaviour, but I'm still confused about the neutral voltage. The company that installed the furnace is being great about everything, I'm just trying to help my buddy get to the bottom of this. Also it's a great learning opportunity for me, I find it really interesting.


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## CanadianSparky (May 10, 2011)

I can't see this voltage affecting the furnace and not any electronics in the home?


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## Duke55 (Oct 4, 2011)

Ha Ha thanks Big John, it's good to hear someone else has the same opinion as me about the "dirty ground". That was the main reason I went to take a look at it, he lives about two hours from my place. When he told me about the "dirty ground" it sounded like "your problem not ours" kind of solution, which it still could be I guess.


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## Duke55 (Oct 4, 2011)

I can measure voltage on the neutral at the furnace, the furnace disconnect, but can not read it back at the panel. It's a straight run from the disconnect to the panel and nothing else on the circuit. I don't know if that means anything


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## Big John (May 23, 2010)

If it's reasonably low voltage (a couple volts or less?) and it gets lower the closer you get to the panel, that seems normal to me. I expect you're just reading voltage drop on your neutral. The more current you put through that neutral the more voltage drop you're gonna read.

This might explain why the voltage from neutral-to-ground seems to change depending on how the fan is running.

-John


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## mrmike (Dec 10, 2010)

I also think dirty ground is a bunch of B.S.. I don't think is has anything to do with the neutral either. Otherwise, The other parts of the furnace would have problems also.

I would check the control wiring on the Plenum switch which starts the fan at a certain temperature. And check out the switch itself. It should be open at the contact upon start up, and closes when it reaches its temp setting..........................


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## 76nemo (Aug 13, 2008)

Big John said:


> If it's reasonably low voltage (a couple volts or less?) and it gets lower the closer you get to the panel, that seems normal to me. I expect you're just reading voltage drop on your neutral. The more current you put through that neutral the more voltage drop you're gonna read.
> 
> This might explain why the voltage from neutral-to-ground seems to change depending on how the fan is running.
> 
> -John


 
Bingo........


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## RIVETER (Sep 26, 2009)

Duke55 said:


> The only thing that I can find is on the board I'm getting 27v across all terminals except between r and y1 terminal I'm getting around 12v... The y1 terminal is for cooling. Oh and the problem is intermittent it comes and goes between 8 and 12 hrs


Check all joints for good connection. The y1 should read 24v to the common. It is for the AC contactor coil...the unit outside.


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## Duke55 (Oct 4, 2011)

The y1 connection is for the AC, I've isolated the AC unit and get a Voltage reading of 11.2v y1 to common. I can't figure this out, my first thought was that the board is toast but it's a brand new board. I've isolated everything off the board other than the power supply and still get this reading.


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## Duke55 (Oct 4, 2011)

Again thanks to everyone for the help, this definitely gives me some other things to look at when I go back to take a look at it.


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## RIVETER (Sep 26, 2009)

Duke55 said:


> The y1 connection is for the AC, I've isolated the AC unit and get a Voltage reading of 11.2v y1 to common. I can't figure this out, my first thought was that the board is toast but it's a brand new board. I've isolated everything off the board other than the power supply and still get this reading.


Go back to the 24 volt transformer...disconnect the secondary load...then measure the voltage across the secondary.


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## Duke55 (Oct 4, 2011)

I got 27v off the secondary of the transformer which I thought might be a little high, replaced the transformer and got the same.


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## RIVETER (Sep 26, 2009)

Duke55 said:


> I got 27v off the secondary of the transformer which I thought might be a little high, replaced the transformer and got the same.


27 is in the ballpark. Are we working on the furnace or the AC?


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## Roadhouse (Oct 16, 2010)

If it is a newer high efficiency I'm betting it is an electronically commutated motor aka variabale speed. There is a computer module in this motor that literally memorizes conditions. That module is fried if what you say is true, that it's blowing in high speed only and not low speed in heating as it should. 

Close to a grand for that motor and worth every red cent but you can replace only that module at less than half that cost and still worth every red cent. 

Your friend needs a surge protector installed for that furnace. It is too expensive to continually let surges screw it up, me thinks.


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## Duke55 (Oct 4, 2011)

The Furnace... What i'm concerned about is if there is a problem that is blowing the board up, which in turn causes the erratic behaviour. During the odd times that it seems to be working fine there is no neutral voltage... but I didn't check the y1 voltage when it was operating fine. The more I think about it, if the board was blown I would assume that it would not go back to normal operation, but you know what they say, never assume.. lol


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## ce2two (Oct 4, 2008)

Duke55 said:


> I got 27v off the secondary of the transformer which I thought might be a little high, replaced the transformer and got the same.


With power supplies 24vdc,27 volts no load,24 volts loaded!


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## Roadhouse (Oct 16, 2010)

This is a typical ecm motor. The back housing holds the module.









And this is where the problem lays.


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## Duke55 (Oct 4, 2011)

Thanks Roadhouse... That sounds very interesting, do you think that could have anything to do with any neutral voltage?? Also do you think that module could act up intermittently?

I totally agree about the surge protection. I told him that I would install one for him the next time I went to see him. Do you have any preferences on type/brands like I said before I mainly do industrial and very little residential stuff just wondering if you got any suggestions for that? Thanks again.


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## Duke55 (Oct 4, 2011)

Wow thanks for the pics Roadhouse that's awesome. This is my first time posting on this site, and I can't believe what a great resource it is.


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## Roadhouse (Oct 16, 2010)

There are thermistor type resistors as a part of that module, work on temperature. They have been known to fry for far less than a power surge. 

yes, I'm about 99% sure that the motor is your problem and is causing the leakage and whatnot on the neutral. An up to date hvac technician will have meters specifically designed to test the motor, like I have.  Obviously the windings are good as it's coming on, the problem is it's not switching speeds. Switching speeds is internal to that module ONLY.

27 volts is absolutely normal on the control side, btw.


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## Duke55 (Oct 4, 2011)

Can't thank you enough Roadhouse... I just talked to my buddy and he says that the motor is always on high speed, and then it will stay on indefinitely regardless of a call for heat or not. Thanks again, Now I really want to go check that motor out.


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## 76nemo (Aug 13, 2008)

Roadhouse said:


> There are thermistor type resistors as a part of that module, work on temperature. They have been known to fry for far less than a power surge.
> 
> yes, I'm about 99% sure that the motor is your problem and is causing the leakage and whatnot on the neutral. An up to date hvac technician will have meters specifically designed to test the motor, like I have.  Obviously the windings are good as it's coming on, the problem is it's not switching speeds. Switching speeds is internal to that module ONLY.
> 
> 27 volts is absolutely normal on the control side, btw.


 

Usually damaged by cavity degradation. WTH are you going about this placing voltage on the neutral?


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## Duke55 (Oct 4, 2011)

So I guess next step is to check that module, and install a surge protector.


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## 76nemo (Aug 13, 2008)

Duke55 said:


> So I guess next step is to check that module, and install a surge protector.


A surge protector for what? Are there MOV's in the control?? Where are you going with this?


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## Duke55 (Oct 4, 2011)

I'm thinking that a whole house surge protection is a good idea, seeing as this is the second furnace, third board, and all the trouble happened after they had a big storm and blew out a quarter of the town. I mean what could it hurt?


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## 76nemo (Aug 13, 2008)

Duke55 said:


> I'm thinking that a whole house surge protection is a good idea, seeing as this is the second furnace, third board, and all the trouble happened after they had a big storm and blew out a quarter of the town. I mean what could it hurt?


 
Couldn't hurt anything, I just hate to see you use it as a sell point for their problem. I'm not buying it. If you want to yank the PCB, I can tell you how to easily prove it wasn't spiked. There is MOV protection in the board itself. When the board is spiked, the MOV's go. It sure as heck isn't sticking the motor in high gear.


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## mgraw (Jan 14, 2011)

The dip switch settings on the board need to be checked for proper settings. 
The motor needs to be checked with an ECM motor tester.
The static pressure needs to be checked. A dirty filter or evaporator coil could cause problems. Poor duct design can also cause these units to not work properly.
The temperature sensor needs to be tested.

While I agree with Big John that a dirty ground is not likely the cause of this problem many of these type of units will not run without a ground.


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## Frank Mc (Nov 7, 2010)

As Nemo says there,s MOV,s onboard (3 off) ...Im guessing that heat sink is bolted to a triac..?? which could be shorted causing the motor to run full bore....Unless theres some electronics under the pcb it looks like it could be easily fixed...

Good Luck....

Frank


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## oliquir (Jan 13, 2011)

Frank Mc said:


> As Nemo says there,s MOV,s onboard (3 off) ...Im guessing that heat sink is bolted to a triac..?? which could be shorted causing the motor to run full bore....Unless theres some electronics under the pcb it looks like it could be easily fixed...
> 
> Good Luck....
> 
> Frank


yep i have seen that often that some triac just shorted out


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## Roadhouse (Oct 16, 2010)

Duke55 said:


> Can't thank you enough Roadhouse... I just talked to my buddy and he says that the motor is always on high speed, and then it will stay on indefinitely regardless of a call for heat or not. Thanks again, Now I really want to go check that motor out.


 
Yup. Now if it's staying on indefinitely then you might also want to check the high temperature limit switches. There is more than one, on the blower housing and in the heat exchanger chamber and probably one or two more elsewhere in the cabinet. The switches are wires in series. You'd have to check the wiring diagram to see where they are located exactly. 

What these switches do is sense excess heat. When one (or more) trips the blower stays on high speed without any call for anything, heat will not work period, as the motor is trying to force that excess heat from the furnace without producing any more heat so the call for heat intermittenly is disabled.

Some of these switches reset themselves, others you have to replace. The temperature that these switches function at are labeled on the switch themselves. If you do end up needing to replace one or more of these high temperature limit switches make certain you get the same temperature range switch as what's in it already. 

Good luck.


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## Roadhouse (Oct 16, 2010)

The limit switch. On high efficiency furnaces the draft inducer motor may also have one of these on it's housing.


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## Duke55 (Oct 4, 2011)

Thanks everyone for all the info, I really appreciate it. I'm a little confused, and maybe I have something wrong here. I'm thinking that the Voltage on the neutral (0.5v - 6.0v) is not a normal condition. When the furnace is operating normally this voltage is not there. When the furnace is acting erratic (Blower motor stuck on high) I find the voltage on the neutral (0.5v-6.0v). So I'm thinking that I am looking for something that could be responsible for both conditions. Could something on the control side, or on the board be creating BOTH these conditions??


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## Roadhouse (Oct 16, 2010)

Best bet at this point is to have your bud call an hvac technician out. There are too many specialized computerized parts that you can't test that he will be able to and I can only guess over the net. 

Did you test that motor or module? All you realy have to do is pull the entire blower motor housing out after remiving all wiring and harness', remove the motor from the blower wheel and pull the motor out. Once out, just a few screws to remove the rear housing to get to the module. Check for burn marks.


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## Roadhouse (Oct 16, 2010)




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## Duke55 (Oct 4, 2011)

I haven't had a chance to go look at it, he's 2hrs from my place. He's had the guys that installed it out a couple of times, and they have been in touch with the York reps. They can't figure out what's wrong with it, and the York reps are the ones that keep saying "dirty ground". Anyhow last I heard they were talking about replacing the entire furnace, which probably isn't a bad thing. If I get to his place soon I'll check it out, if not I say let them put a new furnace in, I don't see the downside of having a brand new furnace.. lol. Thanks again everyone. Take care Roadhouse thanks for your help, talk to you later.


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## RIVETER (Sep 26, 2009)

Duke55 said:


> I haven't had a chance to go look at it, he's 2hrs from my place. He's had the guys that installed it out a couple of times, and they have been in touch with the York reps. They can't figure out what's wrong with it, and the York reps are the ones that keep saying "dirty ground". Anyhow last I heard they were talking about replacing the entire furnace, which probably isn't a bad thing. If I get to his place soon I'll check it out, if not I say let them put a new furnace in, I don't see the downside of having a brand new furnace.. lol. Thanks again everyone. Take care Roadhouse thanks for your help, talk to you later.


Who, here, can explain what a "dirty" ground is?


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## Roadhouse (Oct 16, 2010)

Nope, nothing wrong with a new furnace, especially a "free" one. Granted I'm not sure the warranty on said furnace but as with all hvac equipment the warranty does not begin anew meaning even though a new furnace will be put in the warranty expires on the original and same date of original new furnace install warranty expiration, whenever that was. 

In other words if the original new furnace had a five year warranty and was installed two years ago then when this new furnace goes in there will only be three years left under original warranty.

Let us know what happens.


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## Roadhouse (Oct 16, 2010)

RIVETER said:


> Who, here, can explain what a "dirty" ground is?


 
Dirty grounds account for flame sensors not sensing the microamp signal through the flame to the cabinet moreso than anything else and thus cut off the call for heat. Three times and then the furnace locks itself out. 

Yippy skippy, cowboy.


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## RIVETER (Sep 26, 2009)

Roadhouse said:


> Dirty grounds account for flame sensors not sensing the microamp signal through the flame to the cabinet moreso than anything else and thus cut off the call for heat. Three times and then the furnace locks itself out.
> 
> Yippy skippy, cowboy.


I was in charge of 20- 1,000,000 btu furnaces. I never had anything go wrong that I would conjure up a problem such as, "DIRTY" ground. How does that occur?


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## Roadhouse (Oct 16, 2010)

RIVETER said:


> I was in charge of 20- 1,000,000 btu furnaces. I never had anything go wrong that I would conjure up a problem such as, "DIRTY" ground. How does that occur?


 
A loose or absent ground or neutral. Very common in residential furnaces.


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## EJPHI (May 7, 2008)

Any chance of getting your clamp-on amp meter around that neutral?

EJPHI


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