Furnace won't work on battery

[dbusse]

I can't get my Suburban NT20SQ furnace to work when running on the batteries. I have dual deep cycle batteries that are both fully charged (V ~ 13.6V) and two full bottles of propane. The furnace works perfectly on 120Vac but won't ignite when running on batteries. The blower comes on but the heater never ignites.

Any ideas what might be wrong?

Thanks,
Dave

[onequicksportster]

Are you sure you have L.P supplying it? Try purging to your stove eye, once you have gas there, turn off the stove eye, and try the furnace again..

[fonzie]

Disconnect your shore power, start furnace and check voltage at battery while furnace is running and it should be above 12 volts. That will tell us if battery capacity is good or not.

[dbusse]

Guys,

Thanks for the reply. I've already purged the propane lines. When on shore power the battery voltage measures ~ 13.2+V (can't remember exact value - trailer in storage). The deep cycle batteries are new and fully charged. Battery voltages have been confirmed w/ both volt meter and trimetric battery monitor. Both meters agree that the batteries are nominally 13.5V+.

Dave

[bubbles]

Originally Posted by dbusse

I can't get my Suburban NT20SQ furnace to work when running on the batteries. I have dual deep cycle batteries that are both fully charged (V ~ 13.6V) and two full bottles of propane. The furnace works perfectly on 120Vac but won't ignite when running on batteries. The blower comes on but the heater never ignites.

Any ideas what might be wrong?

Thanks,
Dave

When on shore power the converter (12V) is powering the furnace and since the blower comes on when off shore power the battery input to furnace seems ok. Not sure where the switch over between converter and battery input to furnace occurs. I'm with you, seems strange why one and not the other. Setting thermostat to higher temp?

[dbusse]

I've adjusted the thermostat up to 85 degrees. The blower responds correctly but I get no response from the igniter (when on battery). Everything works great when on shore power. I'm thinking that maybe the controller board is bad?

Dave

[alparmer]

Originally Posted by dbusse

Guys,

Thanks for the reply. I've already purged the propane lines. When on shore power the battery voltage measures ~ 13.2+V (can't remember exact value - trailer in storage). The deep cycle batteries are new and fully charged. Battery voltages have been confirmed w/ both volt meter and trimetric battery monitor. Both meters agree that the batteries are nominally 13.5V+.

Dave

A fully charged battery is ~12.6v. If you are reading more than that then the batteries are being charged. Being that the furnace works on shore power but not on batteries means you don't have a gas problem. It sounds like you have a problem with the transfer switch. It provides 12v to the furnace through the converter while on shore power, but maybe not switching over to battery after disconnecting it. Also, make sure your batteries are fully charged. Measure them without shorepower hooked up, engine running, or on generator power.

Edit: just read that your blower is running. I wouldn't think it's your board since it works fine while on shore power. Not sure how the igniter system works, but maybe it requires a certain voltage before it even attempts to fire and the blower does not...and if the blower is running, and your batteries are low, then the blower is dropping the voltage even lower.

Dunno, start with getting a good reading on your batteries.

[Ford Idaho]

Start it on shore, then unplug the power, what happens?

[OldCoot]

Sounds like a defective gas valve if the batteries are full charged.

[KyDan]

Originally Posted by OldCoot

Sounds like a defective gas valve if the batteries are full charged.

Explain how the defective gas valve works fine on shore power and not
on battery power??

I'm with most of the crowd here- You need to measure the
voltage AT the furnace when on shore power and then again on battery
power.
The only thing I can imagine making it act like this is low voltage when on
battery power.

[Herk7769]

Originally Posted by KyDan

Explain how the defective gas valve works fine on shore power and not
on battery power??

I'm with most of the crowd here- You need to measure the
voltage AT the furnace when on shore power and then again on battery
power.
The only thing I can imagine making it act like this is low voltage when on
battery power.

My money is on a corroded terminal at the current limiter near the umbilical service box. A poor connection here will result in reduced voltage to the camper when operating on battery (even when the batteries check good at the battery.

OR

A bad or corroded ground connection at the frame. Follow the black/white wire from the battery to the frame.

[Still Kickin]

Originally Posted by alparmer

A fully charged battery is ~12.6v. If you are reading more than that then the batteries are being charged. Being that the furnace works on shore power but not on batteries means you don't have a gas problem. It sounds like you have a problem with the transfer switch. It provides 12v to the furnace through the converter while on shore power, but maybe not switching over to battery after disconnecting it. Also, make sure your batteries are fully charged. Measure them without shorepower hooked up, engine running, or on generator power.

Edit: just read that your blower is running. I wouldn't think it's your board since it works fine while on shore power. Not sure how the igniter system works, but maybe it requires a certain voltage before it even attempts to fire and the blower does not...and if the blower is running, and your batteries are low, then the blower is dropping the voltage even lower.

Dunno, start with getting a good reading on your batteries.

I agree that if your reading 13.2v+ your reading batteries under charge mode. Unplug from shore, turn some lights on to take the surface charge off the plates in the bats, then take a reading. Should read 12.7v if at full charge.

[OldCoot]

Originally Posted by KyDan

Explain how the defective gas valve works fine on shore power and not
on battery power??

I'm with most of the crowd here- You need to measure the
voltage AT the furnace when on shore power and then again on battery
power.
The only thing I can imagine making it act like this is low voltage when on
battery power.

Might work on 13.2 volts but not on 12.5 volts. Stranger things have happened.,

[Herk7769]

Originally Posted by OldCoot

Might work on 13.2 volts but not on 12.5 volts. Stranger things have happened.,

Makes sense; the minimum voltage for it to work is 12.0 volts if I recall correctly. If the solenoid is corroded, it could require a more voltage to get it to move.

[Joe_GA]

All good info here. Have you checked the voltage at the heater when the blower is on? Battery voltage is meaningless because the voltage could be good at the batteries and low at the heater due to bad/corroded connections.

[dbusse]

Thanks everyone. I'll pick it up from storage and look closer at the electrical contacts & measure voltages at the heater.

Dave