Furnance wont work


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Old 12-04-09, 06:09 PM
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Furnance wont work

I live in wisconsin, in a mobile home, with a Nordyne model MMHA-070ABHR-01 that uses natrual gas. it will kick on and the hot surface ignition system works. it lights the pilot and senses the flame and turns off. the pilot stays light for a bit but right before the main blower kicks in it goes out. what could be causing this?
 
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Old 12-04-09, 07:18 PM
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The pilot orifice may need cleaning. And also clean the flame sensor while at it. Seattle Pioneer, in one of the recent threads, gave how-to advice on this subject, where the general principles should apply. You have to get the whole pilot assembly out of the furnace, to get at the end of it.

More and more Wisconsinites are coming to this forum, I have been noticing.
 
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Old 12-04-09, 07:37 PM
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ok i will try that and let you know. thanks for your help cuz it gets cold here and even us wisconsinites cant take it lol
 
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Old 12-04-09, 07:38 PM
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Originally Posted by ecman51`

More and more Wisconsinites are coming to this forum, I have been noticing.


Winter seems to bring them out.


During the summer, we are chopped liver around here!
 
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Old 12-04-09, 07:47 PM
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lol umm what recent thread was that posted in? i cant seem to find it lol
 
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Old 12-04-09, 07:57 PM
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wait i found it but is that gonna work when i have a hot surface ignition?
 
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Old 12-04-09, 08:00 PM
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Originally Posted by SeattlePioneer
Winter seems to bring them out.
Yeah. My computer says 18 degrees out.(windy too, with trace snow blowing about) What about you?


During the summer, we are chopped liver around here!
That's when I jump ship and go over to the AC forum.
 
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Old 12-04-09, 09:23 PM
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Unhappy

ok i took it out and cleaned it and it didnt help. the HSI works and lights the pilot by glowing red then when the piolet is lit the HSI stops glowing. then its in warm up mode (lol dont know what else to call it) and the flame stays lit while a moter at the bottom of the vent is humming. then all of a sudden even before the main blower comes on everything dies. then right away it repeats this cycle, over and over again til you turn it off. now when i cleaned off the HSI (which really wasnt dirty just looked lighter du to flame) i didnt see what on it could be a flame sensor so im guessing its internal. now should i just try replacing the whole HSI and see if that works? or could it be something else?
 
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Old 12-04-09, 09:32 PM
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Sounds like this may be a Honeywell Smartvalve ignition system, Ecman.
 
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Old 12-04-09, 09:38 PM
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it doesnt say it honeywell anywhere on it
 
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Old 12-04-09, 11:02 PM
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Old 12-05-09, 06:47 AM
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Old 12-05-09, 10:40 AM
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ok so im thinkin now that its the control board. lol ive been on google all day and havent found alot on what could be the problem but this is how everything goes...


1) thermostat calls for heat

2) draft inducer motor starts

3) hot surface ignitor starts and glows red

4) click is heard from gas valve and burner lights up

5) hot surface ignitor stops glows and cools down

6) burner has a steady flame

7) and this is where the main blower is supposed to start up but it doesnt. the red light on the control box is not blinking which means no codes (unless it doesnt do that)

now ive been thru all the wiring and no where can i find a flame sensor or a thermocoupler but the furnace has been working fine since we moved in here 7 years ago.

now my buddy who works on commercial furnaces came by to see if he could fix it but couldnt figure it out. he did check all the wires and said it looks set up weird to him. but he also said he isnt familar with mobile home furnaces. he did meter everything to see if it was working properly and he said we lose 120volts when the blower is supposed to kick on.
 
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Old 12-05-09, 11:01 AM
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See if you can take some picture of the circuit diagram that are good enough to be able to read.

Also some pictures of the burner compartment and the circuit board and anything else that looks interesting.

I haven't been able to find a manual on your furnace on the internet and that makes it difficult.
 
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Old 12-05-09, 11:06 AM
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Originally Posted by Duffy
I live in wisconsin, in a mobile home, with a Nordyne model MMHA-070ABHR-01 that uses natrual gas. it will kick on and the hot surface ignition system works. it lights the pilot and senses the flame and turns off. the pilot stays light for a bit but right before the main blower kicks in it goes out. what could be causing this?

Here you are talking about a pilot light, but the only ignition system that has a hot surface ignitor and a pilot light that I know about is the Smartvalve system which you don't have.

Are you talking about a pilot light or the main burners?

Your friend seems to be a pretty competent guy. As I understand you, he found no 120 volts switch on to operate the fan motor.

That certainly implies that whatever should be turning on the fan isn't working properly, and that may be the circuit board as you suggest.
 
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Old 12-05-09, 02:49 PM
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So now the way you describe it (somewhat different from your OP, which sounded like it shut off at the pilot stage, and never even got to the burner stage), it sounds like everything works up until when the blower should come on, but it don't. Generally, the furnace should keep running with flame and inducer running until it high limits, which should take at least probably a couple minutes minimum. How long is the burner going for, before the gas valve shuts down? Does the indcuer keep running?, or shut off?
 

Last edited by ecman51; 12-05-09 at 03:07 PM.
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Old 02-21-10, 05:00 AM
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Sounds like the same problem I had. I could turn the fan from auto to on and it would begin heating the house. After 15 minutes or so, I could reset the fan back to auto and the fan would automatically turn on and off. I then replaced the two fan limit switches, one at a time, and found that the L140-40F (part number 6262792) was at fault. I also found this link Intertherm LP gas furnace--fan cycle. - http://www.hvacmechanic.com/ Forums to another possible solution
 
 

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