Suburban NT-32A furnace help needed

[new owner]

Our NT-32A Suburban furnace is having issues. Here are the symtoms...We can light the pilot light and it stays lit. Everything seems like it works well through the first cycle. The fan goes on, the burner unit starts up, we feel heat, the burner unit goes off, the fan continues to run for a while and then turns off. When the temp goes below what the thermostat is set at you'd expect the process to start all over again, it doesn't! The fan might turn on for 20 or 30 seconds, but then it tuns right off. No heat! We have found if we push in the reset button it will kick off the burner and we have heat. I have looked in our owners manual, but not being too mechanical I have yet to find this issue in the troubleshooting guide. So far we have replaced the thermostat (didn't know if we needed it, but it was cheap!) We purchased a thermocouple (we didn't install it) but since the pilot light stays on we aren't convinced that is the issue either. Any suggestions out there? Much appreciated!

[idroba]

There are a couple of possibilities, both hard to find to be sure. There is an over limit Klixon thermostat like device inside the heating section of the furnace. When the air temp goes over the pre set limit of it, it turns the burner gas off. They are somewhat unreliable, especially on older units. They cool down and should re establish contact, but don't, and the furnace will not fire properly on the next start up. The second possibility that comes to mind is the relay inside which controls various functions. They can get old and tired too.

I don't think you have any thermocouple issue, as your pilot light remains lit. Your sail switch is working, or you would not have heat at any time. What I don't understand, because I have never seen or heard of the problem is that "The fan might turn on for 20 or 30 seconds, but then it tuns right off". I can think of no reason for that on the old non electronic ignition furnace you have. (oops, on re reading prior to posting, I thought of a reason, could be the anticipator in the thermostat is set too "fast" and all you are getting is a relatively quick heat demand then the thermostat turns off from the anticipator)

I know I can sound like a broken record on this issue when I post, but any 38 year old furnace can have so many issues, some safety related, that you might consider replacing it with a new one. Often you fix one thing and another crops up. If you are not big on taking the furnace out, working on it, putting it back in, having it work (maybe) and repeat, think about replacement. On those years and models of Suburban Furnaces there was a long standing recall for a defective crossover tube which was fixed in a recall. However, if yours was not fixed, it is still a safety issue, and Suburban no longer has the recall parts available, nor do they support any parts for those furnaces.

A new furnace will have electronic ignition, so no more pilot lighting. It also will probably have a somewhat lower current draw from the fan motor, good if you camp without power available.

[new owner]

Thank you very much! The decision to fix or replace just got a whole lot easier. Believe it or not, the previous owners kept a 3 ring binder with everything in it - including the recall letter. I read it, but didn't understand it. Thank you for the explaination. I'm thinking a new furnace is in my future