Atwood 7916-II furnace

Model: Aliner Classic
Year: 2006
Description of Problem: The problem is with my Atwood 7916-II furnace. It always run on the 12v system but 95% of the time it doesn’t run when the camper is plug to outside power supply either from Honda 3000 generator or house source. Would it be an electrode problem or the circuit board. Although it always works when not plug in.

Our Answer

Hi there: It sounds to me like you have a convertor problem. When you plug in the 110VAC line the convertor is supposed to disconnect the battery supply to the trailer, but normally allow the battery to charge,(if it is the type that charges your battery). At the same time in this process the convertor output replaces the battery output for all DC requirements onboard the trailer, lights, furnace etc. All your lights etc. then should operate from the convertor power and you can check this by noting if your lights brighten a bit when the power cord is plugged into 110 V power. If so this same power should be available for the furnace to operate. The next check would be to see if when the furnace is running on battery, plug in to see if it stays running. The electrode and module board only provide the spark and gas valve operation, and there should be no difference on 12v or 110vac, as you would still of course be running on 12VDC as far as the furnace is concerned. If things do not work as I have explained, most convertors have a relay that operates to disconnect the battery when energized by the 110vac, but also makes up contacts to switch over, and you could have a faulty convertor in that regard.

Hope this will help.
Bob

Follow Up

My Converter (WFCO 8725) is the type that charges my battery.

Yes the lights get brighter once it is plug into outside source.

Also if i am running from the battery and plug into outside source it will go on for maybe 3 or 4 time igniting on 110 volts for an hour or so then after a while will shut the furnace and it won’t start unless I go back to the battery only. I have also seen it go on by the outside source first for a few time and then after “3 times of not igniting” will shut the furnace off. I then have to go to battery only!!!!

Thanks

Our Answer

Hi: Well you do have a unique problem. Module boards are usually such that they work or they don’t, they are not self correcting the same as any solid state devices. The igniter is only used to start the burn, unless the igniter probe does not stay in the flame after lighting, a higher voltage (110v on ) may give a slightly faster fan speed and may tend to lift the flame away from the igniter sensor probe. If your igniter has three probes on it one will be the sensor probe and that one must stay in the flame to provide the electrical circuit to pass through the flame to return the info to the board that the flame is truly lit, to keep the gas valve turned on. The newer models have only two probes and the igniter probe is used to complete the circuit, The other is the ground probe just fastened to the igniter base. You should be able to tell if you have one or two wires going to the igniter, the new ones only have one which is the high voltage or spark wire. The operation is the board sends out a voltage to the probe, which passes through the flame to ground to keep the board energized If the current fails due to loss of flame or perceived loss of flame the board will shut the gas off.  If you are able to see the flame while it is operating this will help to determine if this is happening. Keep in mind this voltage is micro/millivolts and the current is milliamps so there is no way to measure it. Par of you igniter probe could be burned off causing this problem.

Hope this will help.
Bob

Follow up

Hi Bob

The weather was cold today but no rain so I did some testing. (if you remember from my notes that the furnace runs every time on the 12volt battery but always on the 120 volt outside source.

1st Step

I disconnected the battery and plug in the outside source and check all the readings of the fuses I was getting 13.71 DCvolts.

I then remove the “30 amp reverse protection fuse” and was getting no readings on the other fuses except 13.88 on the left side on that 30 amp fuse.

Which seems that every thing seem to be ok with the “convertor”.

2nd step

I then put in the 15amp fuse that runs the furnace in and turn it on and it “wouldn’t light up” or kick in.

After reading your notes a few time, you talk about the electrode/probe and check to see if the lights get brighter on 120 volts supply.

I had also notice that the “Furnace Fan” goes a lot faster in comparison to working on the 12 Volt battery only.

So I kick the furnace on and it still wouldn’t light so I went outside at the “exaults of the furnace and held a piece of cardboard at an angle and “voila” the furnace kick in every time. That tells me that the fan is running to fast on the 120Volt supply and as you said if the gas doesn’t ignite it shuts itself off. Does that make sense to you.

Would it be a “electrode/Probe igniter” problem like a crack igniter probe or not position correctly.

I notice that there is only one wire going to the electrode/probe.

Thanks

Our Answer

Hi: I would doubt that the igniter would be cracked, but obviously the air speed is too high for the flame/sensor issue. Either the sensor/igniter, (as it is the same piece of equipment with only one wire to it) is partially burned off, (shortened), or somehow has dislodged or moved although very unlikely. You would either require a new electrode, or adjust the one you have so it stays in the flame when running on 120V supply. If you are unable to see it’s position while running it is very hard to tell, and the electrode itself may be quite brittle if it is well used, and not adjustable. My guess would be a new electrode would solve your problem. They are available at a cost of around $20.00 plus taxes and shipping. The electrode has two prongs, one being ground the other with the wire connection. These prongs run parallel to each other but the one with the wire attached has a bend at the spark end to bring it closer to the ground probe. These are usually about 3/16 of an inch gap but if one is burned off the gap could be larger, it might still spark OK but may be out of flame proximity when the fan is blowing, as the fan blows in fresh air for burning and can distort the flame enough to pull it out of range.

Hope this will help.
Bob

Follow Up

Good morning Bob

Does the electrode come with a gasket or is that to be ordered separately?

I call Atwood yesterday for the part number of the probe/electrode. (Part # 37517)

I have put the camper in storage for the winter. I will go at this in the spring.

Now do you have it in stock. I may go for a drive if not to far away before.

Thanks a million for the great advice.

Our Answer

Hi again: No I do not have it in stock, and it does not normally come with the gasket as for the most part they are salvageable. If you decide in the spring let me know as we are now basically closed for the winter. I am always available for assistance, but we just shut down the physical operation for the winter.

Have a good winter.
Bob

Follow Up

Thanks Bob

I will get back to you in the Spring.

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