Suburban Furnace won't ignite, help

[hornethauler]

Good evening

I just purchased a 2004 Keystone Hornet 24RS. I am have a problem getting the Suburban furnace to light on 12v. It will fire up every time when the 110V a/c is hooked up.

I will start from the top.
Like I said with 110V it fires right up. When only the 12v battery is connected the blower fan will come on but it will not ignite and the blower shuts off in about 30 seconds. I fully charged the battery, load tested the battery and it's good. Had the auto parts store load test the battery and charge it and it's good. After the Auto parts store charged it I hooked up the battery and the furnace fired right up, once and then it would not ignite.
I have ohmed and toned all the wires from the breaker box to the furnace, to the switch and they all tone good. All grounds look good that I can find. I replaced the 50amp breaker at the battery outside, cleaned the ground at the frame next to the battery box and replaced the corroded cable ends.

Every thing else on 12v works great
I have 12.4v at the battery
11.9vdc at the furnace
10.9vdc at the furnace when the blower comes on.
According to the suburban manual I am with in proper VDC for the furnace to ignite.

when the A/C is connected I have 12.4VDC at the furnace and it drops to 11.7VDC when the blower kicks on.

So all grounds look good, battery test good, wires tone good and all external connections are new. Works great on A/C power and converter.
Other than a battery that is fooling me I am totally stumped.

This has beat me down and need some help.

Thanks
Shane

 

[Ron]

I recommend you start at the battery and remove the negative cable  and clean the post and connection then do the same with the positive leaving the grn disconnected til you have the pos reconnected.  Then follow the negative cable back to where it connects to the frame and remove and clean that connection.

 

[hornethauler]

Ron thanks for the quick reply.

I have cleaned all terminals and replaced all the cable ends. I did move the ground at the frame and used a new self tapper screw with a new cable end. I will double check that tomorrow.

 

[Ron]

Another thing is if you can get hold of another known good fully charged battery try that.  Sound like low voltage on battery is your problem.

 

[Karl]

The difference between 10.9(battery) and 11.7(120) at the furnace could make all the difference in the world. I would suspect that the blower is not turning fast enough on battery power to activate the sail switch, which determines whether the furnace will light or not. Remove the outside furnace cover and check for any obstructions in BOTH parts of the blower assembly (combustion air and heated air) and the burner flue, lubricate the blower shaft bearings. Also make sure nothing is blocking any of the air ducts inside the rig; both heated air ducts and cold air returns. The sail switch itself may have accumulated enough dirt to make it too heavy to operate properly. Check and clean, and make sure it operates freely. Also, a voltage drop of 12.4(battery) to 10.9(furnace) is not normal, and puts it on the hairy edge of the control board not functioning. The wires may have toned out o.k., but somewhere in the circuit there's too much resistance. Check out all the wiring and, optionally, hook up a 12V battery directly to the control board and see if that takes care of the problem.

 

[Ned]

I would suspect the battery as it works correctly on shore power when the charger/converter is supplying the 12VDC.  Get a load test on the battery.

 

[Weewun]

With Shore Power connected you read 12.4 volts at the battery, seems that the converter should be maintaining around 13.4 volts when charging.  Since you read 12.4 volts at the battery with or without Shore Power it seems to preclude the battery as the culprit.  I do not belive the Converter is suppling sufficient output to fully charge the battery but enough to keep the voltage at 11.7 volts while the furnace is running.

I do not know if you converter has adjustments but it should be supplying around 13.4 volts to charge the battery.

 

[hornethauler]

Yes with Shore Power the furnace works great. I have never tested the voltage at the battery with the shore power connected so I don't know what the voltage is there.

Today I will triple check all the grounds, pull the sofa and furnace shroud and check for obstructions, lube the blower shaft and go from there. check voltage at battery with shore power connected. I will most likely be buying a new battery, it's cheap insurance IMO. It seems to me that the battery is the weak link even though all load test come back good

Thanks
Shane

 

[Gary RV_Wizard]

I concur with all the advice about the battery. 10.9V with the fan running is NOT sufficient for reliable ignition.

Sounds to me like the battery is not taking much charge, despite the load test result. By the way, auto store load tests are geared for starting loads, which is high current but short duration (5-15 seconds, depending on the tester). I would not put a lot of faith in it, since all other indications are contrary.  A direct jumper wire from battery to the furnace power terminals would prove that out, though.