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Old 11-25-2008, 08:59 AM   #1
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Problems with new furnace..Overheating, having to reset. Furnace too big?


Some backround first. Cliffnotes on the problem below.

OK..Heres the story.

I installed my own propane furnace. I had oil heat, but had an old oil tank, and wanted a cleaner fuel anyways.

So, out goes all the oil stuff..Put in a new propane furnace. It is a Tappan 100,000 btu high eff 92%. I ran 3" intake and exhaust piped to outdoor air(good slope whole way). 3/4 iron to the furnace. Put the new orifices in for the propane conversion, and spring per the instructions
I read the instructions probaly 100 times and had the furnace checked out by the propane company. Everything regarding the install is fine - but just wanted to get that out of the way.


So I have the tank installed.
The propane company checked manifold pressure after the gas valve and found it at 10. (in spec)

They fired the furnace. Ran great. They left, went on there way...and I assumed everything was over with.

Well, the furnace just started blowing cold air a couple hours later after cycling a couple times. Hit the roll-out switch..and then it would burn a flame.

I ended up buying a digital t-stat and set it to only cycle twice an hour. We have a fairly drafty house and its pretty hard to keep it at one temperature. So thought that could help some.

I also opened up some of the air intake duct work near the furnace. That seemed to help a lot more cold air get in. (All the vents are open BTW).

Then I increased the blower speed. (switched the M1, M2 wires on the control board to M2, M3) The instructions didnt show how to do this exactly..but I think thats how its done. Seemed to blow a little harder.



So anyways..after doing these things, it still will start blowing cold air and tripping the roll out switch. May be fine for several hours, or a day or 2. I can only assume its from overheating. Ive checked the flame..It looks fine(goes where its supposed to, etc..)

I just switched from a dust-free filter to a typical fiberglass one. Should flow better. We'll see if that helps..but not counting on it.

Is it possible this furnace is simply too big for my house? It is 2500 sq ft..and fairly drafty. I have 15 or 16 warm air vents. The propane techs did say the furnace looked too big for the house(100,000 btu), and that I needed atleast 13 warm air vents to expell the warm air. (so figured I was covered).

I also noticed the overheat switch made a clicking noise(activiated) when I was working on the furnace once. I had my halogen light shining on the furnace about 7 fft away from it..and that set it off! It seems too sensitive.

It also activated once and blew cold air after the furnace had been off 10 minutes or so - no call for heat(you'd assume it'd be cooled down by then)..And the blower runs after the flame goes out, just enough to get to cool air. (i.e. normal..)

If the furnace is too big - should I just add another warm air duct? I can easily add one right by the furnace to the basement area.

Otheerwise, I had another idea..If the switch tripping is legitimate(i.e. its getting too hot inside) can I just take out an orifice or 2 and put plugs in those outlets? Thus making it more like an 80,000 btu unit. My guess is that I can't do that..but thought it was worth mentioning.

So theres the whole long boring story. Hoping to get some help..Went this far without hiring someone. Id hate to now over something simple like this..

I should mention too that I have 2 working carbon monoxide sensors in the house(never went off..incase someone is thinking bad heat exchanger)


Cliffnotes:
Furnace blows cold air sometimes..Have to hit roll-out switch. Is it possible furnace is too big? Or should I buy a new switch? Should the gas press be checked again?

Last edited by Tommy2; 11-25-2008 at 09:54 AM.
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Old 11-25-2008, 10:02 AM   #2
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Problems with new furnace..Overheating, having to reset. Furnace too big?


sounds like its as simple as a bad rollout sw. being over or undersized has no bearing on the rollout. thats there to protect you from carbon monoxide or dirty heatexchanger or any situation where the flames could leave the heat exc.
and based on your story you stated its tripping when the unit isnt running, sounds bad to me

located inside the cabinet on the rating sticker you should see the words heat rise than a temperature value for example:45-75
this means when the unit is running and up to operating temp, the differance between return air and supply air should be between 45-75 degrees of each other. example:ret/air temp 70. supply air temp125
as long as youre within this range your furnace isnt over/under fired.
make sure you dont take a temp reading where there is any infared heat
for example take your reading several feet away from the furnace

Last edited by kennzz05; 11-25-2008 at 10:11 AM.
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Old 11-25-2008, 10:07 AM   #3
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Problems with new furnace..Overheating, having to reset. Furnace too big?


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Originally Posted by kennzz05 View Post
sounds like its as simple as a bad rollout sw. being over or undersized has no bearing on the rollout. thats there to protect you from carbon monoxide or dirty heatexchanger or any situation where the flames could leave the heat exc.
Thanks for the reply. I'll probaly go ahead and buy one. (should be cheap enough) before putting anymore time into it.

The flames look good..but, its somewhat hard to see all of them clearly through the little eye piece. And I cant imagine how they could not be going into the heat exchangers. Slipping the manifold/orifices in place was pretty much idiot proof.
Unless the gas press changed after the furnace fired a few times. (it said in the instructions to adjust the press after firing a few times..gas company did it only once)
But they do this all day everyday..So you'd think they got it right.
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Old 11-25-2008, 10:25 AM   #4
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Problems with new furnace..Overheating, having to reset. Furnace too big?


Just did it again..Furnace was off for five minutes. Then the blower started up. (no call for heat)

So I guess I should replace the roll-out switch.


The temperature coming out of the furnace feels "normally" warm. Basically the same as the old oil unit.
The air duct on top the furnace gets warm, but not to where it would burn you. Pretty much what you would probaly exepct.

Also, the furnace exhaust (and intake) 3" pvc blow/suck fine..Condensate is fine as well.

Oh, and I felt the burner cover where the roll out attatches to. It does not get very warm when furnace is on. About the same warmth of the ducts.

Last edited by Tommy2; 11-25-2008 at 11:57 AM.
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Old 11-25-2008, 03:21 PM   #5
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Problems with new furnace..Overheating, having to reset. Furnace too big?


[quote=Tommy2;189931]Some backround first. Cliffnotes on the problem below.
..

I should mention too that I have 2 working carbon monoxide sensors in the house(never went off..incase someone is thinking bad heat exchanger)
Just because the carbon monoxide detector didn't go off doesn't mean that the heat exchanger isn't bad. A flame rollout is serious and should be checked by a professional. You went this far and saved alot of money,so if you want to be safe and live to tell about it have it checked by a professional. Manual resets are there for a reason(to get your attention that there is a problem)
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Old 11-25-2008, 03:25 PM   #6
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Problems with new furnace..Overheating, having to reset. Furnace too big?


A bad heat exchanger on a brand new furnace? This switch doesnt actually "detect" carbon monoxide, right? Its just senses heat? And the panel its mounted to does not get beyond "warm".

Talked to the supplier I got the furnace from. He told me to notice the code flashing on the control board. It just looked like a continuous flash..But Im running the furnace again to see if it can trip the code again, just to make sure.

Of course, now for the first time its working perfectly and I can't get the roll out to trip again lol. Running fine the past few hours set a few degrees higher than before too.

I pulled out the roll-out and looked it over. Maybe just handling it a bit, knocked something loose in it so its working right.

I cant get over how flimsy these switches are. Im a car guy, and Im just shocked at how flimsy some of this crap is. That switch is a joke. The button is just loose feeling.

Last edited by Tommy2; 11-25-2008 at 03:28 PM.
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Old 11-25-2008, 06:44 PM   #7
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Problems with new furnace..Overheating, having to reset. Furnace too big?


Are you sure its not pulling its own exhaust back in.
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Old 11-25-2008, 07:10 PM   #8
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Problems with new furnace..Overheating, having to reset. Furnace too big?


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Are you sure its not pulling its own exhaust back in.
Hi, No, shouldnt be. The pipes exit the house with the exhaust on top, intake below. The intake has a 90* downward termination, and the exhaust has a 45* horizontal termination.
Not quite cold enough to see the exhaust real well, but I'll check it again when its colder out..Then you can see the warm exhaust much better.
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Old 11-25-2008, 07:19 PM   #9
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Problems with new furnace..Overheating, having to reset. Furnace too big?


You didn't change the motor speed correctly which could account for the intermittent tripping.

Nordyne (Tappan)is my line so I can speak with some authority here.

Look in your instructions on how to change motor speeds and take a temperature rise from the supply and return.

Also describe how you ran the PVC with how many elbows per each run.

Post the distance between the out door terminations.

Been there could be right too, it may be recirculating exhaust wind the wind changes.

Get back to us with the info i posted.


Also possible to have a bad LP regulator.
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Last edited by hvaclover; 11-25-2008 at 07:24 PM.
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Old 11-25-2008, 07:37 PM   #10
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Problems with new furnace..Overheating, having to reset. Furnace too big?


Quote:
Originally Posted by hvaclover View Post
You didn't change the motor speed correctly which could account for the intermittent tripping.

Nordyne (Tappan)is my line so I can speak with some authority here.

Look in your instructions on how to change motor speeds and take a temperature rise from the supply and return.

Also describe how you ran the PVC with how many elbows per each run.

Post the distance between the out door terminations.

Been there could be right too, it may be recirculating exhaust wind the wind changes.

Get back to us with the info i posted.


Also possible to have a bad LP regulator.
Thanks for your reply.

How do you change motor speeds on these Tappans? Could you please explain it?
In the instructions it says "please refer to your furnace instructions for how to change the blower speed" THOSE ARE THE INSTRUCTIONS!
So, I just assumed it amounted to moving the leads over.
There is virtually no information on how to change the motor speed other than the wiring diagram.

What exactly did I do by moving the leads over?

The PVC run is fine. Its about 20ft each pipe 2/3 bends per pipe. Upward slope, etc, etc. By far within spec since I used 3 in pipes.

The distance between outdoor terminations is probaly over a foot. Its possible the winds could effect it some, and the intake could get a slight breath from the exhaust..but would that effect the switch tripping after the furnace is done cycling?

I do not have a thermometer to check vent temperatures. (guess I need to get one) I can only assume that I need a higher than factory fan speed (or atleast it wouldnt hurt anything) when using a fairly large (possibly oversized) furnace.

Last edited by Tommy2; 11-25-2008 at 07:40 PM.
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Old 11-25-2008, 08:11 PM   #11
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Problems with new furnace..Overheating, having to reset. Furnace too big?


Jeeze...
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Old 11-25-2008, 08:17 PM   #12
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Problems with new furnace..Overheating, having to reset. Furnace too big?


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Jeeze...
What did I say?

If theres any Nordyne experts - please describe how to change blower speeds properly. Ive been searching the net, and can't seem to find anything.
Can't believe it's such a mystery heh.
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Old 11-25-2008, 08:22 PM   #13
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Problems with new furnace..Overheating, having to reset. Furnace too big?


i said "Jeeze" cause i just dawned on me I am under legal obligation to my furnace line not to go beyond what advice I have already given you.
Sorry.

The directions can be obtained from who ever you bought the furnace from.
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Old 11-25-2008, 08:26 PM   #14
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Problems with new furnace..Overheating, having to reset. Furnace too big?


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Originally Posted by hvaclover View Post
i said "Jeeze" cause i just dawned on me I am under legal obligation to my furnace line not to go beyond what advice I have already given you.
Sorry.

The directions can be obtained from who ever you bought the furnace from.
Well, thats no problem. I just wanted to make sure I didnt offend you somehow!
(dont want to upset anyone).

At anyrate..I think I actually might understand it now. The m1, m2 and m3 terminals are "unused". The instructions say this, but I didnt understand why.

To adjust the blower speed, you have to palce a different wire into the "heat" tap. Which makes perfect sense. Looks like black for high, blue for medium high, orange for medium low, and red for low(the current wire).

So, I should get a good thermometer and set the speed correctly.

The instructions were a joke for this though. Zero direction..

Last edited by Tommy2; 11-25-2008 at 08:30 PM.
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Old 11-25-2008, 08:29 PM   #15
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Problems with new furnace..Overheating, having to reset. Furnace too big?


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Well, thats no problem. I just wanted to make sure I didnt offend you somehow!
(dont want to upset anyone).

At anyrate..I think I actually might understand it now. The m1, m2 and m3 terminals are "unused". The instructions say this, but I didnt understand why.

To adjust the blower speed, you have to palce a different wire into the "heat" tap. Which makes perfect sense. Looks like black for high, blue for medium high, orange for medium low, and red for low(the current wire).

So, I should get a good thermometer and set the speed correctly.
:thum bup:
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