furnance trouble

It's fairly easy to test the limit switch. Just locate the switch, and put a TEMPORARY jumper across the two connectors. Then fire up the furnace and try it. Don't leave the jumper on for other than testing, as it leaves no protection against overheating.

Though I support Dinosaur boards myself and, owning one, I have looked at it with all the training and expierence I have (Certified Electronics Tech Licenside Ham Radio operator going on half a century,, Just put a 36 year old radio back in service,, complete with a repair or two). and the feeling of QUALITY looking at those boards was amazing, IT IS THERE.. OEM board, (much more expensive) not so well built.


That said: I think you need to look to the high-temp cut off.. 20 seconds is control board, 2 minutes sounds more like high temp cut off.

IF that is the problem, it may be your ducts need to be cleaned out.

Teacher's Pet wrote:
1st place I would look would be the control board. "Dinosaur" boards are great for fixing old furnaces and water heaters with operation problems. Example .... Dinosaur Electronics after market repair boards. Caution .... Make sure you order by your furnace model number not by the model year of your RV.

I got it bookmarked just in case I'm hoping for the best. Thanks for the post. will let you know what I find out. I have to keep the old rig rolling .:)

Itasca55

punomatic wrote:

Itasca55 wrote:
I have a 1992 Itasca sunrise 27ft with a suburban furnace . Is this a big fix or small fix . what its doing is you turn it on heats up fan starts blows heat2-3 mins and 5 mins heat stops even though It should stay on as thermostats telling it to stay on all that comes out is cold air. It started this last year . We used electric heater to get by but this year I would like to fix it . Any advise be great . :?

Itasca55

Since you don't give a model number, I can't get you directly to the manual for your model, but click here then scroll down the page to the list of Furnace Service Manuals, continue scrolling to the Suburban manuals and find the one for your model. You can open the manual online or download it (note: files are large). Suburban includes a detailed troubleshooting section in their manuals. I have used it several times with success every time at getting the old heater to run again.

Thanks a bunch . There great manuals. mines SF 20-25-30-35 I have to wait till snow milt to get to it. As sheds a bit full winter storage we had a warm spell and now back to cold . I think its a 30 . It be great to get it working again . It heated great 2 years ago . But mine is 1992 model just so hope its not what i read in the notes. ( if all is clean and burner keeps going out replace control board ) That be nasty but I will check everything else first. :D thanks again and this is a great forum . I will post my findings .

Itasca55

Jagtech wrote:
Another possibility is the high limit thermostat cutoff inside the furnace may be bad, cutting out at a low temp, after a few minutes of heating. Cheap fix.

That would be my bet. When mine was malfunctioning due to wasp nests, the fan would come on but there would be no heat (sail switch wouldn't close). If the fan is running, and it's getting warm, and then shuts off then it's probably the limit switch. Could be a defective switch or it could legitimately be getting too hot for some reason.

Another possibility is the high limit thermostat cutoff inside the furnace may be bad, cutting out at a low temp, after a few minutes of heating. Cheap fix.

Itasca55 wrote:
I have a 1992 Itasca sunrise 27ft with a suburban furnace . Is this a big fix or small fix . what its doing is you turn it on heats up fan starts blows heat2-3 mins and 5 mins heat stops even though It should stay on as thermostats telling it to stay on all that comes out is cold air. It started this last year . We used electric heater to get by but this year I would like to fix it . Any advise be great . :?

Itasca55

Since you don't give a model number, I can't get you directly to the manual for your model, but click here then scroll down the page to the list of Furnace Service Manuals, continue scrolling to the Suburban manuals and find the one for your model. You can open the manual online or download it (note: files are large). Suburban includes a detailed troubleshooting section in their manuals. I have used it several times with success every time at getting the old heater to run again.

From my experience all three of the first three posts are spot on. Thermostat calls for heat, fan comes on, sail switch closes which opens the gas valve, the board says I need ignition, gas burns and then you got hot air. If the burner tube has something blocking it the supply of gas is diminished and the flame may not get hot enough.

I have found that some service mgrs. will have their techs check the board for a few bucks. It takes about 5 mins, once they get to it. If you want you can buy your own board tester for about $80. If you need a new board, Dinosaur is the best from what I have learned here and from the pros.

And to answer your question, some heaters are really easy to repair, it depends on where they put the board. The burner tube and the board are usually assessable from the outside behind the heater louvered door.

furnace should not heat up then fan goes on,should not be possible unless sail switch is stuck,if you are not familuar with opperation get a pro,the few dollars you save wouldn't be worth what could happen.

Before replacing any parts, I'd suggest checking for airflow problems thru the burner.
Spider webs and mud dauber nests are common and can restrict the airflow.

Take the outside cover off, clean everything you can see with a brush and a vacuum, see if that helps.
There is a "sail switch" that measures airflow and locks out the burner if there is not enough, since your unit does fire, that is probably not the problem, but I think you have to take the inside cover off the furnace to get t it.