suburban nt30sp furnace

[lazer50]

Hi fellas. I have a 26 ft camper i use at my shop over winters it has a suburban nt30sp furnace running off propane.ive had the camper 3 years,the first year the furnace seemed to work fine until the latter part of winter then the unit would ignite and run the burner would shut off the fan would stay running blowing cold air until i woke up freezing and shut the furnace off.i could restart the furnace and it would ignite and run and same thing happened so i ended up using auxiliary heat that year.the following fall i pulled furnace cleaned igniter set gap at 5/16 also cleaned squirrel cage fan assembly found some debris thought that was problem.when installed last fall and tried same problem.i have had gas pressure tested and leak tested in camper.haven't changed any components on furnace.any help before winter greatly appreciated as i plan on using camper this winter. Thank you!

 

[Fixin'Stuff]

Sounds like you just need to clean the flame sensor. It's a thick wire, usually mounted in a ceramic base, that is in the direct path of the flame from one of the burners. They build up an oxidation layer over time. A quick cleaning with a wire brush will usually get things going again.

The sensor is there to turn off the gas if the unit is calling for heat but no fire is detected. It's to keep you from either blowing up or waking up dead.

 

[lazer50]

Are you referring to the ignitor?i thought when the thermostat sent a signal to the gas then voltage went to the ignitor.i may be missing something but one thing i forgot to mention is sometimes when the furnace does ignite and come on the ignition is LOUD as in boom.

 

[bazar01]

If the furnace has been running for a while then the burner goes out and the combination blower and combustion fan still runs, then it's the limit switch.
The limit switch is an inline device that protects the furnace from overheating. The contacts in the limit switch open at a given temperature setting shutting power off to the ignition system and also controls the gas valve.
It's either the furnace discharge temp is too hot or the limit switch is suspect.
You have to troubleshoot either way. Safety first when working on a gas furnace.

 

[lazer50]

I believe i know what the limit switch is on this unit.maybe i can get some numbers from it and get a replacement.

 

[lazer50]

Is the limit switch referred to also known as a sail switch?

 

[bazar01]

Is the limit switch referred to also known as a sail switch?

Nope.
Sail switch is the equivalent of an air flow switch.

 

[lazer50]

Can i tell which one is which by location?

 

[Fixin'Stuff]

Are you referring to the ignitor?i thought when the thermostat sent a signal to the gas then voltage went to the ignitor.i may be missing something but one thing i forgot to mention is sometimes when the furnace does ignite and come on the ignition is LOUD as in boom.

No. The ignitor is a different part. The flame sensor typically looks like this:

The ignitor lights the fire. The flame sensor makes sure that the fire is really lit. Limit switches make sure that the fire isn't too hot.

If the fire goes out, the flame sensor tells the control board to shut off the gas valve.

If the fire gets too hot or rolls out of the firebox, the limit switches tell the control board to shut off the gas valve.

Home furnaces usually have an LED on the control board that will flash a sequence to let you know what failed. I don't know if your furnace has that feature.

 

[bazar01]

Can i tell which one is which by location?

Here is a manual available online. This should help.
http://www.bdub.net/manuals/Suburban_Service_Manual.pdf

 

[Backpack Hunter]

Are you referring to the ignitor?i thought when the thermostat sent a signal to the gas then voltage went to the ignitor.i may be missing something but one thing i forgot to mention is sometimes when the furnace does ignite and come on the ignition is LOUD as in boom.

With it making a boom upon ignition it is telling you there is a bad gas to air ratio. Common causes are (but not limited to) debris/bugs in the orifice/burner and a breach in the burner tube.
The igniter senses flame and sends that signal back to the circuit board. The circuit board tells the gas valve to open or close.

 

[lazer50]

I want to thank the members for helping me with my furnace issues! I replaced all the gaskets,installed a new fan limit switch,and replaced faulty igniter. Total parts including shipping was 45 buck give or take and that includes new wasp screens for exhaust on oustide of camper.thanks again! According to download sheet for furnace it works as new!