New NT-30SP fires 10 sec. then goes out, fan on

[fotochop]

Installed a new Suburban NT-30SP in my '69 Safari and I'm testing it with the front cover off. Fan comes on, flame comes on but only for 10 seconds or so before going out, fan runs continuously and won't switch off. Since I'm "jumping" the trailer's thermostat (see below) seems like the unit should be ON (with flame) as long as the 2 thermostat wires are connected.

(Unit arrived with only one blue thermostat wire showing. Schematic showed second (blue) thermostat wire connected to red 12V wire. I added this second thermostat wire myself, then jumped the thermostat by connecting the two blue wires together. Correct me if I'm wrong here, but I think I'm ok with that. Sort of a 'bench test' but unit's still in the trailer.)

Any help appreciated.

Rick Olivier

[bryanl]

sounds like the overheat switch, maybe.

fan on says thermostat calling for heat. that's OK. typical of old style controller boards to leave fan on as long as thermostat is calling for heat, no matter the burner status.

furnace wouldn't fire if sail switch wasn't working

but 10 sec before flame-off is rather short for most overheat switch problems. That safety usually gets worked when duct air flow is too low to remove furnace heat. Poor duct flow seems to be almost a norm in a lot of trailers.

[Inland RV Center, In]

Originally Posted by fotochop

Installed a new Suburban NT-30SP in my '69 Safari and I'm testing it with the front cover off. Fan comes on, flame comes on but only for 10 seconds or so before going out, fan runs continuously and won't switch off. Since I'm "jumping" the trailer's thermostat (see below) seems like the unit should be ON (with flame) as long as the 2 thermostat wires are connected.

(Unit arrived with only one blue thermostat wire showing. Schematic showed second (blue) thermostat wire connected to red 12V wire. I added this second thermostat wire myself, then jumped the thermostat by connecting the two blue wires together. Correct me if I'm wrong here, but I think I'm ok with that. Sort of a 'bench test' but unit's still in the trailer.)

Any help appreciated.

Rick Olivier

You cannot properly test the furnace with the front cover off.

Andy

[fotochop]

Thanks, Andy, I had a feeling that might be causing problems. I'll try it again with the cover on and see what happens. I was fortunate to find a Suburban manual here:

Service Documents

the same place I found my (old) Dometic refer manual, and it contains a lot of valuable information..in case others may be searching for manuals/troubleshooting, etc..