Problem with furnace, help needed!

Questions about repairs and parts for Nordyne furnaces, air conditioners and heat pumps for manufactured homes including Intertherm, Mac and Miller brands. Click here for Nordyne parts.

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bobthebuilder
Posts: 4
Joined: Sun Nov 15, 2009 2:08 pm

I have a Nordyne FG6RA-045C-08A furnace with control board PT#624631-B 1012-955A.

Red LED on control board stays constant on, as it should when properly running. No blinking/error codes are ever given.

After getting a signal from t-stat, the inducer turns on for 30 secs, then turns off. No ignition. No gas. The pressure switch goes from open to closed when the inducer is on, as it should.

The good:
All safety switches are closed.
Transformer is outputting 24-27v.
The ignitor looks fine, <2 years old.
The furnace itself has been rarely used for its ~2 year lifespan. (maybe this should be in the "bad" column.)

The bad:
Ignitor wires/plug never goes to 120v at any point in cycle. Stays at 0v, with ignitor connected or not.
Although pressure switch goes from open to closed when its supposed to, I'm only reading 5vac, not 24vac. (5v from terminal to terminal on the pressure switch when open, 0v when closed. Supposed to be 24v when open correct?)
The voltage of the two wires that go to pressure switch, measure the same 5vac when disconnected from pressure switch, so the switch itself has nothing to do with the odd 5v.

I appreciate any and all help. This seemed like one of the better forums I've come across. It seems to be a bad control board, since I'm getting an odd voltage from the pressure switch circuit. Thanks for you time!
Bob
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Robert
Moderator
Posts: 6413
Joined: Wed Feb 28, 2007 12:07 am
Location: Tennessee

Hi Bob,


Got an idea of possible problem, let me pull up your wiring diagram and will get back with you in a few.


Thanks,
Robert
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Robert
Moderator
Posts: 6413
Joined: Wed Feb 28, 2007 12:07 am
Location: Tennessee

Hi Bob,

Do you know if you have a variable speed blower motor or just a normal 2, 3 or 4 speed motor ?



Thanks,
Robert
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bobthebuilder
Posts: 4
Joined: Sun Nov 15, 2009 2:08 pm

Thanks for the reply!

It is a normal 3 speed motor I believe.

Thanks again for the help!
Bob
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Robert
Moderator
Posts: 6413
Joined: Wed Feb 28, 2007 12:07 am
Location: Tennessee

Hi Bob,


One more question, is it an upflow or downflow furnace ? Need this to look at correct wiring diagram.

There 4 different ones, but this info will give me one I need.



Also, test across R and C on control board for 24vac. Then, WITH a call for heat from t-stat, test across W and C for 24vac.



Thanks,
Robert
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?
bobthebuilder
Posts: 4
Joined: Sun Nov 15, 2009 2:08 pm

Hi Robert,

It is an upflow furnace.

R and C = 24vac
W and C, standby = 5vac
W and C, with call for heat from tstat = 24vac for a split second, then back to its normal 5vac

The inducer does get engaged by a call for heat and runs for 30secs.

Thanks so much for your help.
Bob
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Robert
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Posts: 6413
Joined: Wed Feb 28, 2007 12:07 am
Location: Tennessee

Hi Bob,

Turn power to furnace off, remove cover(s) to t-stat, disconnect RH and W wires and tie them together. Restore power and see if you get continuous 24vac across board W and C.

Also, does furnace start up and run ok ?

IF so, reply back. IF still same across W and C and furnace still not working, do this :


Turn t-stat to OFF and fan switch at t-stat to auto. remove cover(s) to reveal wiring.

Test across RH and W for 24vac and see if it reads 24vac for a minute at least.

Then keep the leads there and have someone set t-stat to call for heat.

See if RH and W changes from 24vac to 0vac and remains that way for a minute or more.



Thanks,
Robert
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?
bobthebuilder
Posts: 4
Joined: Sun Nov 15, 2009 2:08 pm

Hi Robert,

I tied RH to W, got a continuous 27vac across W and C. It runs fine and the cycle completes now, unlike before, so after the 30sec inducer stage it continues with ignition, gas, then flame.

I tested your second method too, if it may help. Across RH and W I get about 22vac, which correlates to the 5vac W has normally and the 27vac RH has normally. When called for heat, for a split second it goes to 0vac, then back to the 22vac.

So it seems the 27vac I should be getting on W constantly during the heating cycle, isn't contant, and only goes to 27v for a split second, which I guess is long enough to start the inducer to go on, run for 30sec then turn off. The "split second" of 27v also corresponds to a relay on the tstat I can hear click. Heat is called, then a split second later the relay clicks and at the same time the voltage goes from 27 to 0v on W. So it seems the relay is switching, when it shouldn't. Is the 5vac on W normal?

Tstat is a Luxpro PSD111
duke62
Posts: 1
Joined: Sat Nov 14, 2009 3:33 pm

hi have a problem witha norydene furnace model m1mb070a down draft ,it starts up and runs fine and then it shuts the fan off for a second or two and turns it back on you can hear the combustion motor running seem to only do it when its cold and the t stat is set on about 75 replaced the t stat,and both limit switches any idea's
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Robert
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Joined: Wed Feb 28, 2007 12:07 am
Location: Tennessee

Hi Duke,

Please start a new thread with your questions and then delete your post here. We do not allow but one poster per thread to keep down confusion.


Thanks,
Robert
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?
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Robert
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Posts: 6413
Joined: Wed Feb 28, 2007 12:07 am
Location: Tennessee

Hi Bob,

Your t-stat is bad and needs replaced. Stay away from all Lux and Hunter t-stats. Get a Honeywell, White-Rodgers or a Rite-Temp if cost is a big factor.



Thanks,
Robert
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