furnace

Pulled cover to access furnace and checked voltage which was 11 amps checked connection at furnace seemed ok , noticed that during the manufacturing process the extra wire length on the furnace had been pinched between the wall and a ledger board to hold up the bottom shelf for the refer to set on used flat bar to remove wires and tried furnace has started and run for 1 1/2 days now, not what happened I am continuing to do the other things suggested. Thanks again for the help.

We really need the model of the furnace- a huge number of the DuoTherm 659 series had transformers in them for shore power use, and a built in "transfer relay" to switch to battery, or a manual switch.

Regardless- that furnace is a minimum of 20 years old, so it really needs to be pulled out and inspected. At the very, very least, buy a good CO detector.

replace the 30 amp fuse coming off the battery

Also check that there is no dirt buildup on the sail switch blade. I've seen a few with just enough cooking grease/dirt buildup that the extra volt or so from the converter was needed to run the fan fast enough to trip it. The battery voltage alone wasn't enough.

I suspect you hav a dirty connector. It seams 12.7 v at the battery is not enough for the fan to run fast enough. 13.6 is . Pull the connectors and clean(the shop should have done that)

When you check the voltage at the furnace, check it while the furnace is trying to start. However, since the furnace starts on shore power and generator, I would suspect the connections to the battery, or the battery itself.

Definitely sounds like 'low dc voltage' problem.

Fan comes on but on runs for a 15 seconds then shuts down......
Fan has to get up to at least 75% of rated speed in order to close 'sail switch'. If sail switch doesn't close no further action can occur (power to circuit board, then ignitor/gas valve).
With low dc voltage fan speed not enough to make up sail switch

DC voltage is present at all times from fused position on dc dist panel. Goes from panel to timed delay relay.
DC power also goes to t-stat then back to furnace. When t-stat contacts close power is applied to fan motor. Sail switch makes up....power then goes thru high limit switch then to circuit board. Then board sends power to ignitor and gas valve for igniton of main flame.
Power is getting to motor but not to board for ignition when on battery source.

Need to check voltage at furnace when on battery source and that grounds are good, tight and clean (at furnace and from battery).


Incorrect dc polarity will also cause main flame to drop out shortly after ignition........can't hold gas valve open.

And don't give anymore work to that shop :R

donn0128 wrote:
Check voltage at the furnace with the shore power disconnected. I suspect it will read low voltage.

ditto, 13.78 VDC most likely was when the converter was running from shore power or generator. 12.7 VDC is about most you should see from fully charged lead acid batteries UNLESS being charged.

Check voltage at the furnace with the shore power disconnected. I suspect it will read low voltage.