furnace blower cycles on and off

[hvac-tech05]

Hello, I am working on a mobile home furnace, it is a Homemiller furnace down flow. The problem i am having is, the blower motor keeps on cycling on and off. when the burners lit the furnace heats up and i can watch the fan limit heat up and turn the blower on then the burners shut off and the fan continues to run until the fan limit cools down and the blower shuts off, then i can watch the fan limit heat up again without the furnace liting and it will kick the fan back on until it cools back down. it will continue to do this every minute all day long. i have read some post with similar problems but never really nailed the problem. the whole furnace was cleaned, the air flow is good and i adjusted the fan on and fan off settings, i set the cut in at 140 and the cut out at 90. any help would be greatly appreciated.
thanks

[Twilly]

Twilli says the answer is in this song....

[temco]

Are you a HVAC tech? This is a pretty basic problem. Your furnace is shutting down on high limit and fan is coming back on because it is not cooling down enough. Since your not sure what to do you need someone to look at it who knows how to diagnose it as it could be a safety issue.

[Flash9]

Got to love those spiders, but unless they are lighting matches I don’t see how the limit will continue to heat up all day long without the burner coming on.

[cmajerus]

Seen too many homes burnt up from those old "Home" furnaces, they look great in the dumpster out back.

[beenthere]

Get post count up, and apply for pro membership.
And post questions like these in the pro tech forum, where they can be answered.


There is more then one limit on most MH furnaces.

[pctech]

Home miller is a nordyne miller furance it used to be called home miller for some odd reason miller or intertherm furances are the best furnaces for manufatured homes you can get .
sorry twill colemans dont last

Seen too many homes burnt up from those old "Home" furnaces, they look great in the dumpster out back.

[aircooled53]

There is a reason that the unit is going out on high limit ,and you need to call a professional serviceman to check your unit before you have fire.

[clintkennon]

Home miller is a nordyne miller furance it used to be called home miller for some odd reason miller or intertherm furances are the best furnaces for manufatured homes you can get .
sorry twill colemans dont last

It seems to me every time I go to a Manufactured home the fans out because there's 3 feet if dirt on everything. I don't know why but people around here just don't want to change the filters in those furnaces.

[hvac-tech05]

i dont think i am making myself clear. the furnace isnt cycling on high limit. the furnace runs thru a cycle and once the fan limit cools down to 90 degrees the fan shuts off, now at this point i watch the fan limit creep back up to 130 degrees and the fan will turn back on and it will cool back down to 90 degrees but there is no call for heat at all. so what is happing is the heat exchanger isnt cooling down and staying cooled down.

[aircooled53]

i dont think i am making myself clear. the furnace isnt cycling on high limit. the furnace runs thru a cycle and once the fan limit cools down to 90 degrees the fan shuts off, now at this point i watch the fan limit creep back up to 130 degrees and the fan will turn back on and it will cool back down to 90 degrees but there is no call for heat at all. so what is happing is the heat exchanger isnt cooling down and staying cooled down.

Ok, then WHY is the furnace getting to hot or is the fan limit control BAD.
Did you check temperature rise and check gas manifold pressure,indoor coil clean ,filters clean blower running at design speed.All these things need to be check before you move temperature settings on fan/limit control.Might be that the limit control is old and not sensing properly. But most cycle off at 100*. With it set to cycle fan of at 90* its building back up temps for some reason.

[clintkennon]

i dont think i am making myself clear. the furnace isnt cycling on high limit. the furnace runs thru a cycle and once the fan limit cools down to 90 degrees the fan shuts off, now at this point i watch the fan limit creep back up to 130 degrees and the fan will turn back on and it will cool back down to 90 degrees but there is no call for heat at all. so what is happing is the heat exchanger isnt cooling down and staying cooled down.

Does this happen all day long with the furnace off.

[Twilly]

Twilli obviuosly ate to many mushrooms and made an inaccurate diagnosis. Twilli still likes the song though.