Help please NG furnace?

[1kzwoman]

I have a friend having fan issues with her NG furnace. Thank you in advance for suggestions.
Fan will run past cooling on heat cycle of furnace. Main burner will light .
I already had her check off/on/auto setting on wall switch.
I've seen a thermocouple cause burner not to light but never a fan to run.
Note fan will sometimes cycle properly

 

[razerface]

take the cover off the thermostate and make sure a wire is not loose and touching 2 terminals. If that is ok,,find the relay that turns on the fan,,,it is sticking. Depending on the furnace,,,may have electric eye malfunctioning too.

 

[1kzwoman]

Thank you. The furnace is +-25yr old install original to mobile/ modular. She's in a tough spot so trying to help her, but replacement maybe real cure.
I will check items listed,

 

[razerface]

I was thinking of a modern programable thermostat,,,does she still have the old style round one?

 

[yooperdave]

Could it be that the air filter on the furnace is dirty/plugged and needs to be replaced causing the furnace to go into "high limit" during which the fan only runs?

 

[1kzwoman]

[quite="razerface, post: 1702397, member: 31598"]I was thinking of a modern programable thermostat,,,does she still have the old style round one?[/quote]
No it's been up graded

 

[1kzwoman]

Could it be that the air filter on the furnace is dirty/plugged and needs to be replaced causing the furnace to go into "high limit" during which the fan only runs?

She is running with out filter to my knowledge. I thinks its a Colman furnace but don't quote me. I have only been there at 2am to relight a bit blurry eyed. Wind a factor in that.

 

[heat seeker]

There may be a plenum temp sensor that's flakey. Look for a sensor on the plenum, should have two wires going to it.

 

[WiscWoody]

If she gets any energy assistance she can ask for help with her furnace problems and they may just replace it if not now when funds are available. Even if she doesn't qualify for energy assistance she might get some help from the counties health and human services department.

 

[1kzwoman]

Thank you all so much. She lost her husband to the big C a couple years ago. I just bearly get her to let me help. Pride is about all she got

 

[fbelec]

on most older furnaces there is a gray box mounted some where up high on the furnace. it has a white plastic stick sticking out of the box. it says manual/auto or something of the like if pulled out the fan runs constant if pushed in (at that point still sticking out) runs at what it is set at. the setting or under the cover. take the cover off and watch it go thru a cycle. if it seems to be hanging up then just replace it. not to expensive. three or four wires very easy to replace. these go bad right about at that age.

 

[fbelec]

here is a picture of what i'm speaking of
https://www.google.com/url?sa=i&rct...gg8AZqV1_88RxxS2pRw89nwA&ust=1396050775380071

 

[1kzwoman]

here is a picture of what i'm speaking of
https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=3PldTSQFXl767M&tbnid=MQgkOYCmFJWAAM:&ved=0CAUQjRw&url=http://www.justanswer.com/hvac/49tnk-22-year-old-coleman-furnace-mobile-home.html&ei=ALo0U7e5DdOksQSAiYDIBg&bvm=bv.63808443,d.dmQ&psig=AFQjCNHqXEgg8AZqV1_88RxxS2pRw89nwA&ust=1396050775380071

Thank you again. I thank my Dad for the mechanical and DIY skills he taught me.Many women didn't get the lessons that can only be learned with grease and gojo. It has saved me more than once. Mom had a hard time understanding that gas and oil mix was needed for lawnmower..

 

[heat seeker]

That's what I was referring to! They do tend to stick as they age. That would explain the erratic performance. I couldn't remember exactly what the sensor was, since I last had a hot air system about 25 years ago, but did have trouble with mine.
And, excellent pic, fbelec!