Suburban nt-40 furnace issues

[Charliemomoney]

The furnace just started doing a short cycle. Woke up to cold. Reset the thermostat and it started, it lighted and ran the burner for 5 mins. Then the cool down cycle and stopped. To restart you must either cycle to heat strip or to off and then Bach to furnace. Then the same result. I replaced the battery in the 12 volt system,replaced the propane regulator, replaced the analogue thermostat,replaced the ignitor, still shuts down before the thermostat temp. Is reached. Any ideas ?

[TURBS]

Originally Posted by Charliemomoney

The furnace just started doing a short cycle. Woke up to cold. Reset the thermostat and it started, it lighted and ran the burner for 5 mins. Then the cool down cycle and stopped. To restart you must either cycle to heat strip or to off and then Bach to furnace. Then the same result. I replaced the battery in the 12 volt system,replaced the propane regulator, replaced the analogue thermostat,replaced the ignitor, still shuts down before the thermostat temp. Is reached. Any ideas ?

Try turning off your propane tank valve and waiting a few seconds then very slowly open it back up.

Tank full?


Turbs

[Charliemomoney]

Yes both tanks are full, I am set up for full time use since the 25 th of June 2102 , I went to Las Vegas for Christmas and left the thermostat set at 60. I returned and worked for a week with no issues. Then 1 morning woke up to the cold. There is no o e close who works of anything RV. So I have tried to attempt it. I did find 1guy in bishop Calif. it's 2hours away. He came and pulled the unit, he brought a new board for the furnace, but his did not work at all. He broke the ignitor in the process, so he stole the one from the fridge, and got it working like it was. He came back yesterday and brought the replacement ignitor for the fridge and the furnace and assumed that was the issue. However it was not and he charges 300.00 just for the trip. So I am not going to continue to throw $that direction. , still looking for answers, if all else fails when the temp rises , I will pull the unit and drive it to Las Vegas for a bench test.

[powertrader]

I think I am having a similar problem on my new TT, I have it plugged in at my shop, and have set the thermostat at 60. I am not staying in it, just setup getting it ready to use next month, every time I return the heat isn't still on, i have to turn it off, then back on and it runs again.?

[TURBS]

So did you try what I asked?

[Charliemomoney]

Yes, I turned all propane off relieved the pressure then reopened the valves. Cycled the thermostat from off to furnace, it came on, I also light the stove for 1 minute then turned it off. The furnace lit and ran for about 4 or 5 minutes and the burner went out,but the fan continued the cycle the cool down .I switched the function from furnace to heat strip,and the overhead unit began to blow.

So I assume it is still not working properly!

[caper]

The heat strip is in the overhead unit (AC). It could be bad brushes in the fan motor causing the fan to stop a a dead spot.

[TURBS]

I wonder if you have a bad sail switch.

I'm not sure but in the files section there may be a trouble shooting guide.

Turbs

[Dave_Monica]

Have you checked the fresh air/exhaust ports of the furnace to ensure they are clear? If they're partially plugged, the burner may be kicking out on high temp.

Dave

Edit: Here's a link to a troubleshooting guide I found... http://www.ehow.com/about_5612452_su...formation.html

[Charliemomoney]

i have no problem with the overhead unit, or the heat strip application ,it cycles with the thermostat fine, just the furnace, i did consider the sail switch, but haven't replaced it yet.. thanks

[TURBS]

Originally Posted by Charliemomoney

i have no problem with the overhead unit, or the heat strip application ,it cycles with the thermostat fine, just the furnace, i did consider the sail switch, but haven't replaced it yet.. thanks

Upper left hand of frf web page next to USER CP "files" section.

Turbs

[RodeoGeorge]

The most frequent cause of the problem that you are describing is the Limit Switch.

The purpose of the Sail Switch is to prevent the burner from igniting if there is not sufficient air flow, or to shut the burner off if the airflow drops below the required CFM. Your burner is igniting.

The Limit Switch is just that. The device that limits the temperature of the chamber to a safe level. If the Limit Switch is not returning to the normal (open on some furnaces, closed on others) state, the furnace will not cycle back on until shut completely off and turned back on.

RodeoGeorge

[IllinoisCamper]

I had a similar issue on my Roo 19. I am not sure if furnace is the same model. Documentation is packed away in trailer for the winter. My problem was with the sail switch. Seems like Suburban was having an issue with some sail switches getting stuck open. The control board must sense an open switch when it was not supposed to be and goes in lockout mode. turning thermostat off and back on resets the furnace. The fix for mine was that the service center was instructed by Suburban to trim sail switch. At least that is what I was told they did. Worked fine after that.

[Herk7769]

Originally Posted by wa3pnt

The most frequent cause of the problem that you are describing is the Limit Switch.

The purpose of the Sail Switch is to prevent the burner from igniting if there is not sufficient air flow, or to shut the burner off if the airflow drops below the required CFM. Your burner is igniting.

The Limit Switch is just that. The device that limits the temperature of the chamber to a safe level. If the Limit Switch is not returning to the normal (open on some furnaces, closed on others) state, the furnace will not cycle back on until shut completely off and turned back on.

RodeoGeorge

This sounds like the best answer to me...