Nordyne M7 Two Stage Runs Strange

Hiskid

I'm retired and got a used mobile home above a creek at the edge of the woods to retire in. The old Miller was easy to keep running but it was facing the usual hx issues of older Millers. I wanted to switch to propane so I could have a 20k Blue flame as a back up. I figure I might as well go 95+ and two stage. I worked off and on at my brother's HVAC business so I know my way around furnaces and installations. This two stage Nordyne board seems to have a mind of it's own.

Stat calls, I hear the pre purge happen. It fires up on high and the blower and fire spools down to low which runs for about a minute(supply temp-90-100 deg.) then I hear the valve close and the inducer again comes on then a relight on high I figure and 30 seconds later the blower at high speed. This then runs till the stat is satisfied. The burner drops, post purge and blower runs till it's done. As for the stat it is a HW th8320. I have 0170 0n 9, 240-260 on 3, 0530 Smart response toggled on and 0695 finish on high stage toggled off. I disconnected the black from W2 and it still acts the same. From my understanding of two stage it's supposed to run in low most of the time then finish on high if stat is not satisfied. The furnace has an auto stage that runs on low for ten minutes then finish on high if needed. Should I use the auto stage and set the stat for single stage or is something in the stat settings I'm missing ? Which would be more economical.

Thanks, God bless and a Merry Christmas to all.

Paul S_3

Is the thermostat set for warm air 90 plus systems?.... i would run it either way ....but since you have a 2 stage stat run it so the stat controls the 2 stage firing. I really cant say which one would be more economical.... maybe someone else can chime in

Hiskid

Yes it is set on gas 95+

Ironman

That's not normal. The dip switch has to be set to select thermostat or timed control of the second stage.

Make sure you have a good ground connection all the way back to the electric panel. It may be shutting down because it sees a flame failure.

Hiskid

By the dip switch you mean the auto stage jumper ? It is supposed to be jumpered in the off position. I'll check it tomorrow.

Hiskid

It's all new wiring from the ceiling down. I can run an alternate ground to check that.