Furnace problem

[cjoel]

We are on shore power and just replaced the battery. It is raining and will be tomorrow before I can check anything. I havnt checked the battery but everything is working fine.Except the furnace blowing out hot air.

[cjoel]

Originally Posted by TeJay

Concerning the battery. When you are on shore power there should be 13.7 or higher voltage at the battery(s). If not then your converter is not charging at high enough voltage to keep battery charged. Disconnect shore power and measure voltage at battery. It should read around 12.2-12.6 volts. If not then there may be a problem with the battery being able to accept a charge. When troubleshooting a lot of issues accepting that a new item is working correctly can get you into a lot of trouble. New does not always mean that it is good. It's just makes good sense to check an item before you accept that it is good.
JMTCW TeJay

Im heading to the store to buy something to check the battery .

[cjoel]

Turned off shore power , checked my systems monitor it reads battery full.

[Herk7769]

Originally Posted by cjoel

Turned off shore power , checked my systems monitor it reads battery full.

Without restoring shore power run a DC appliance then check to make sure the top light goes out.

With a "full battery" the top light should not be lit as the surface charge from the 13.7 charging voltage can "hang around" for an hour without a load being placed on the battery.

What is the voltage after a load is placed on it?

Maybe the best indication is to fire up the furnace with just the battery and see where the lights go. If they drop quickly, it could be a corrosion problem with the wires going to the furnace (possibly at the main fuse junction).

OR

It could still be a problem inside the heater (sail switch).

[Mark and Linda]

Been reading the threads, etc., downloaded the PDF file, learning while reading. The fuse in the top photo is for what? I have seen this one under my trailer when I was redoing the wiring insulation and tying things up. I also had to redo some bad connections on the tb.

[Herk7769]

Originally Posted by Mark and Linda

Been reading the threads, etc., downloaded the PDF file, learning while reading. The fuse in the top photo is for what? I have seen this one under my trailer when I was redoing the wiring insulation and tying things up. I also had to redo some bad connections on the tb.

It is the main fuse between the battery and the converter.

Symptoms of this fuse opening are:

12VDC power when on shore power but not on battery alone.
Slides and landing gear work (that green pigtail fuse holder in the photo for example) on battery but nothing 12 volt in the camper works.

If the terminals on that fuse are corroded, the voltage drop can be substantial even if the battery is good.

[Mark and Linda]

Now, I need to go out there tomorrow, crawl underneath and see what size, etc. and see if I have one in my stash of things. Thanks for the info on it.

[caper]

We had the same problem and it turned out to be a bad board.

[Herk7769]

I think, like you, that it is in the furnace, but before I called in a high price repair guy, I would eliminate all the "cheap (I can do it) fixes.

Full DC voltage to the furnace means it is in the furnace and it will need to be removed to troubleshoot. This is not for the faint of heart.

[COcamper41]

I appreciate Lou's suggestions. Actually you can do a solid amount of troubleshooting without taking the furnace out. If you ended up buying a multimeter, you can check voltages at the pins on the mother board.

If you get a multimeter, please share the make and model of your furnace. Just take the cover off, and you will be able to see the make and model.

A few people have mentioned the control board. If you have high enough propane flow and voltage is solidly above 10.5 volts with a little load, then it's a 95% chance it's the mother board. Those suggestions might be spot on. Nice thing is they are easily replaced without removal of the furnace, and you really don't need to give someone $100+ to replace it.

You can check the propane pressure with a manometer, but very few people have one. One or two people suggested turning the burners on your stove and see if the flames are nice and high. It's easy to just turn a couple burners on and assume it's fine. If the propane pressure isn't high enough, the gas valves aren't going to work. Frankly, changing the regulator is a ~$30 job and often it will fix the problem if it's a propane based issue.

Have a good one.

Lon Black
Colorado Camper Rental

[Herk7769]

If you decide to pull it check out:
http://www.forestriverforums.com/for...opy-32377.html

[Goomph]

Originally Posted by herk7769

If you decide to pull it check out:
http://www.forestriverforums.com/for...opy-32377.html

The ones you can take out from outside the trailer must be a breeze. Mine is buried under the fridge and It will be a bear to take it out. At this stage I am pretty sure it is the main board or the relay which is shot. I might change them both just not have to take it out again. Not looking forward to it to be honest.

Looks like OP's furnace has an internal problem .... Wishing him good luck !

[caper]

Ours is under the fridge also and only takes about 10 mins to remove. We had to remove the furnace in order to access the control panel. We were lucky and found a retired repair tech. that did repairs to help with his pension income. He only charged $25/hour. It cost us $150 to have the board replaced. $115 for the board and $35 labour. About a week after the board was replaced the fan stopped running. Found out that there are brushes on the fan. So if you do have the furnace out and get the board changed have them replace the brushes on the fan motor at the same time. It will not cost that much more for labour and the cost of the brushes are not expensive.

[cjoel]

I have ckecked out everything I can without taking it out.I really think the gas line is stoped up ill check that tomorrow.

[cjoel]

Just tried to start the furnace , took the side panel off to see what its doing . When it tries to ignite it lights and emediatly goes out. Because heat comes out the exaust for a second .

[Thurman]

Nice that I found this thread tonight after camping at FDR State Park this past weekend and learning something very valuable about RV furnaces and gas systems. Temps fell somewhat into the high twenty's Friday night. I observed one camper early Saturday morn removing the cover over his furnace and offered to help if I could. He said his furnace had worked flawlessly previously but would not fire up Friday night. We were checking everything we could think of to check when another camper came over to offer his help. He asked as to how much gas was in each bottle on the unit. The bottle the camper was using had been used for a couple of outings but showed green on the selector gauge. Our new helper suggested he change over to his known full bottle, purge the gas lines again and try the furnace. This worked. O.K., so now I'm all confused and asked for an explanation. The lower the ambient air temp, the lower the BTU rating of the gas within the bottle proportional to the pressure of the gas and outside ambient air temp. Well, I had to believe him as he had the furnace working now, but I also had to research this today online and found this to be true. IF, again IF--the amount of gas within an LP gas bottle is low, the ambient temp falls, then the actual BTU rating of the unburnt LP gas will also drop proportionally. Doing the range burner gas flame check will show this as low LP gas pressure, weak blue flame-almost a yellowish flame. The man proved this, in a way. He also told the camper that if he would wrap a blanket around his low tank, place a light bulb under that tank area to raise the temp of the tank just a few degrees, then this low tank just might work again until the tank gets cold again. Google "Atwood furnace service manual" and there is a good chart in there which explains this better.

[Thurman]

One more post here on this subject, something I learned with my camper: I bought mine used everything on it was demonstrated by the seller including the furnace. Here in South Georgia it just doesn't get really cold and one small electric heater kept the unit cozy. Until--one weekend at Veteran's State Park in January when the temps really dipped. NO furnace and the electric heater was not so cozy anymore. I checked all breakers and fuses at the campsite and all were good, but no furnace. After coming home with more time to investigate I found that there was no 12vDC to the furnace although the fuse checked good. Further investigation and I found another 12vDC fuse just for the furnace under the camper at the front where there were other fuses and a wiring junction box. The fuse inside I had checked good was with a volt-meter, not with 12vDC on it. After replacing the fuse in the front the furnace worked just fine. I still do not understand why there is this fuse dedicated to the furnace at the front underside and also a dedicated fuse inside.

[Leroy2u]

Unless I missed it somewhere in an earlier post the furnace mfg was never disclosed. I did have very similiar symtoms earlier this month where the blower would run and no heat (suburban). To make a long story short it ended up being the "limit switch". Basically is a relay the pops when the furnace is working to hard and gets to hot and shuts the furnace down. It is suppose to reset after a couple of minutes and the heating operation resumes without you knowing.

Let us know what the final outcome was of your fix....

[RamblerGuy]

With reference to Thurman's post about someone saying the BTU value of LP changes with temperature, that's baloney. The BTU value is a physical property of the compound. It's the same per pound regardless of the temperature, and it's the same for it as a liquid (aka LP) and as a gas. The volume per pound changes with temperture and pressure changes, but the BTU's per pound does not.

The liquid in the tank has to evaporate into a gas for the system to use it. The heat to evaporate the LP comes from the surroundings, transferred through the surface area of the tank. When the surrounding temperature is low, such as well below freezing, and the usage is high, there may not be enough heat being transferred to the tank to evaporate the LP as fast as it is used, and the pressure would drop. Without looking at some tables and doing some calculations, I won't guess if this would ever be a problem with an RV, but I wouldn't expect it to be a problem until well below freezing. Some of you Canadians could comment on that. It is a consideration when recharging an A/C system with refrigerant, but look at the size of a can of refrigerant and the size of your LP tank. There is only a fraction of the surface area for heat transfer and the drawoff rate is many times faster than an RV appliance, so you have to heat the can in warm water to keep the pressure up.

The LP tank will be at a lower temperature than the surroundings as LP gas is drawn off and more LP liquid has to be evaporated. At times I have seen frost on an LP tank up to the LP liquid level.

[caper]

1. Heat Transfer
   
   
   • Pressurized tanks keep the propane in its liquid form by constantly holding high pressure. So even though the propane is above its natural point of liquidity, -44 degrees, it remains liquid in a tank. In a tank, the propane gets warmer or colder through the heat or cold transferred from the walls of the container. The pressure in the container isn't affected by the amount of liquid in it, but by the temperature surrounding it. Cold temperatures decrease the pressure in the propane tank. This causes a tank to get colder. As a result, it may freeze
     
     
   Low Flows
   
   
   • When a propane tank has very low pressure due to outside temperatures being low, it may be difficult for the gas to flow well. If the pressure is low enough, it's possible the gas won't work properly. This could be a serious problem for someone who depends on propane for heating.
     
     
   Gauge Malfunction
   
   
   • Extremely cold temperatures can cause the gauges on a propane tank to register incorrectly. The addition of a particular amount of fuel may register as less fuel in cold weather, simply because the volume is affected by the temperature. Delivery trucks compensate for these volume differences, but home tanks are not equipped for that kind of measurement. The volume of propane in cold weather will be lower than in warmer weather.
     
     

Read more: How Cold Affects LP Propane Tanks | eHow.com How Cold Affects LP Propane Tanks | eHow.com

Hope this helps.