Furnace will not run after reverse polarity

[myredracer]

Several months ago a friend de-winterized their trailer but he re-installed the battery backwards in reverse polarity. We were camping together and kept smelling a rotten egg smell. Thought it was someone else's sewer. Then we heard a repetitive clicking and then we discovered the battery was in wrong and the noise was the circuit breaker on tongue tripping and resetting.

Everything survived except for the furnace, Suburban SF-30F. Thinking it was the control board, we replaced that today (they got along with a ceramic heater since). But the furnace will not run at all. No fan, no noises, nothing. Measured 13.4 volts are rear of furnace, so that's okay. Tried to simulate the thermostat operating and crossed the t'stat wires together at rear of furnace. Nothing.

One funny thing is that when the thermosat is set to the heat position, the AC unit comes on. Switching it to AC doesn't bring the furnace on but seems to start the AC fan only (would have to double check this). Why would the AC work on heat position? Makes no sense. Is there a relay somewhere that's damaged?

Only other thing I can think of at the moment is maybe the blower motor is shot? Wouldn't explain the AC coming on though on heat mode. Checked the online manual and didn't help.

Any thoughts? We don't want to get defeated by this and have to pay $125/hour to troubleshoot and repair it. He won't be installing a battery backwards again either after this....

[myredracer]

I got the furnace to run. Just need to get it back in to make sure the burner is working fine. There seems to be a jumper wire missing to connect the +12V to the control board. Hot-wired it to make it work. Looked all over for the jumper. Can't be terminals plugged in wrong spots. May have to make up one if they can't find it. (They have a 6 year old that likes to get into everything)

Thanks for the help.

[myredracer]

Reverse polarity fuses did not blow. Found one battery reads 6.0 volts and the other is 7.7 volts. I guess both batteries have been damaged. When the thermostat is turned to heat, it's just the fan in the AC that comes on. As noted above, that may be what it's supposed to do, but friend insists it never did that before. I've confirmed the blower is okay by running 12V directly to it.

Next thing is to double check the wiring connections to the board. Notes were made by same friend that hooked up the batteries in reverse (hmm).... Looked okay at first glance at the wiring diagram affixed to the unit but will look closer.

[subcamper]

There is a lot of DC wiring on my AC unit under the interior cover at the ceiling. Maybe the heat and AC wiring is spliced in there and may also contain a relay or inline fuse . I would remove the AC ceiling cover panel and look there for any clues.

Steve

[JimandMary]

On our 2013 Silverback, the AC comes on with the heater to better stir up the heat from the heater.

[myredracer]

Can't go work on this until later today. Everything else in the TT is working perfectly fine. It's just the furnace that's not working and the seemingly odd thing about the thermostat.

Can anyone say if there is a relay or something for the thermostat somewhere. The t'stat wires that exit the furnace are heavier gauge like may #18 but the wires at the t'stat are small like #28 gauge. Are these spliced in the wall behind the t'stat or do the wires maybe run to something else like a relay in between?

[Wishbone51]

Why would reversing polarity create a rotten egg smell?

[wa8yxm]

IT might also be the thermostat. But I'd check fuses first.

[RoyB]

Anytime I am messing with the battery terminals I always make a mental note to locate the word "NEG" or the symbol "-" on the 12VDC battery case and make sure this is the terminal cable going to the trailer FRAME GROUND which will be close to the battery.

ALot of folks will identify the POSITIVE terminal cables with a BIG RED dot of fingernail polish or maybe take a photo of the connections with the cell phone.

It is very easy to get the terminals crossed. I have even replaced the same brand battery only to find out the manf has flipped the battery terminals. I think they do that to trip you up haha... Now I always look the NEG terminal word on the battery case.

Roy Ken

[RoyB]

When the battery terminals are connected in REVERSE POLARITY it will blow two fuses in the 12vDC Power Distribution Panel labeled REVERSE POLARITY. It will also blow an INLINE FUSE that is mounted real close to the Battery terminal. Sometimes this is a circuit breaker...

A quick thing to remember is that both the ON-BOARD Converter/charger unit and the battery both feed the 12VDC Power Distribution Panel so you can turn on your ceiling lights and some other other 12VDC items when you are on shore power or just running off the battery. If you are NOT able to turn on your Ceiling lights now when running only on the battery this is an indication you have a blown fuse or bad cable connection between the 12VDC Power Distribution Panel and the Battery.

Another way to check this is measure the battery terminals when you are NOT connected to shore power and if fully charged it will read 12.6-7VDC across the battery terminals. Then go plug the trailer into shore power and read the battery terminals again. With Shore Power ON it should read 13.6VDC.. If it doesn't read the 13.6VDC across the battery terminals then this is indicating there is a disconnect between the battery terminals and the 12VDC Distribution Panel.

If you replaced these fuses before changing the battery connections to the correct normal terminals then you have blown the fuses again. Need to correct the battery terminals first then change the blown fuses.

Confirm these fuses are good

Roy Ken

[robatthelake]

There is likely a fuse blown. Check for a couple of inline fuses.