Still struggling with Suburban NT32 furnace

hertfordnc wrote:
So what would make the propane cut out after it was flowing?

Maybe an oil trap in the copper line to the furnace OR intermittent gas valve solenoid coil.

Making progress- I had a modern quick connect regulator that has all sorts of safety features. I changed it out with an old style regulator with copper tubes and bras fittings.

Back at the furnace, 16 seconds after the blower came on there was a spark and a blue flame that lasted about 3 seconds.

So what would make the propane cut out after it was flowing?

newman fulltimer wrote:
It could be anything from dirty connections to a sticking sail switch a bad ignihter a bad propane regulator at the tank and when the temps get down its freezing.
The best thing to do is check the simple things first
1 clean all connections
2 check your regulator see if its good
as if you can change parts you can do this
3 clean the igniter and check that your getting a good spark
4 make sure there is no blockage in the unit

Yep , be sure to check the regulator.
My furnace was sensitve to low propane pressures and wouldn't start. The other appliances were fine. New regulator fixed it.

On an older unit, you will get a bit of voltage drop through the thermostat, limit switch. sail switch, and maybe connections. Often replacing one of these items will let the unit work, but all of the other items can still be causing the voltage drop.
If you have not done so, I would start by replacing the thermostat.

People often say- "It can't be the thermostat, because the blower comes on."
9 volts is enough to trigger the fan replay, which will start the blower, but it is not enough to "fire" the electronics.

To be certain what the problem is would require bench testing.

It could be anything from dirty connections to a sticking sail switch a bad ignihter a bad propane regulator at the tank and when the temps get down its freezing.
The best thing to do is check the simple things first
1 clean all connections
2 check your regulator see if its good
as if you can change parts you can do this
3 clean the igniter and check that your getting a good spark
4 make sure there is no blockage in the unit