Furnace wont reach thermostat setting?

[ajwren]

Hey there. Im having issues with my furnace reaching temperature. I replaced the Thermostat and put new gaskets on the burner box, thinking maybe air was getting in there as previous gaskets had deteriorated. If i leave the door off the unit (front panel) the furnace works great! Reaches temp and turns itself back on when coach cools. But when i put the cover back on it chokes. It heats for a while, then stops and wont come back on. Has anyone got a clue? Limit switch will be next i suppose. Its a Suburban NT-24SP, 30SP, or 34SP. Cant fine a serial number anywhere. Any help would be great. Thanks in advance. Justin

 

[TheLooks]

Furnaces in campers are designed to shut down after a certain cycle. They are not rated for continuous operation. However, it would seem yours is suffering from air flow. This can be input and output constrictions. Since you get better results with the outer door off, I am guessing not enough air is getting to it. But the outside air might be cooler also and making it work better. Check for airflow getting to the furnace, don't block any vents into the furnace or out of the furnace.

 

[ajwren]

Thanks. Ill check again all vents. I believe they are clear tho. But you are right, it sure looks like an air issue. It vents to the floor (when cover is on), straight out when cover is off. Its set to 68. Only comes on 5 degrees. Then stops. It will randomly come on during the night. I can manually keep turning it on. Runs for 3 minutes. Gets warm and then shuts down.

 

[TheLooks]

Ok, you mean the rear cover that encloses the heat exchanger, not the outer cover. Gotch. In this case it is blockages in the output lines. Lets ask how old the camper is and do you have pets? Plus, it can be the high temp limit switch is just opening to soon.

 

[TheLooks]

If it is the switch, it should come on as soon as it cools down if the thermostat is still calling for heat. Furnaces will go into a cool down or purge phase after ignition is stopped for any reason. That should cool the switch down and it should fire right back up. If I were troubleshooting it I would bypass the thermostat to make sure it is not doing something crazy also.

 

[ajwren]

Its not firing back up at all. Unless its a random middle of the night thing. Its the inside cover im talking about. Theres no outside access. Its not the coach screen either. Its the Furnace cover itself. If thats removed it all works as it should. If cover is on it forces air down into the ground and thru the vent system. If off it blows out into the coach. Its a 2007 Fifth wheel.

 

[TheLooks]

Then my guess is something is blocking the output lines in the floor.

 

[TheLooks]

Even so, if the high temp limit is good, it should fire up as soon as it cools down. Jump it out with a fuse, TEMPORARILY, and see if it runs normally. Again.....TEMPORARILY!

 

[ajwren]

Ill try that. Absolutely temporarily! Just to see what it does. Would not run our Furnace like that. Thanks for your help. Ill let you know what i find.

 

[ajwren]

Thanks. I got side tracked here for a few days. Ill get back on it soon. Weather is nice right now. Lol. Thanks again.