Furnace question

[AZsix]

My son and I went camping last night and with temps dipping into the upper 30's heat was needed. We were dry camping running off the battery. I lit the furnace but when I tried to turn on the heat it made noise but no air hot or cold came out. We used it after Thanksgiving when were had hookups and it worked fine. I plugged in just a few minutes ago and started the furnace and it worked fine. There is some kind of issue when running it off the battery. I charged the battery and the lights and water pump worked fine. Is there something I am not doing or is there just not enough juice in the battery to have force the air out?

We got rather chilly last night though not too bad. We could see our breath this morning eating breakfast.

Any ideas?

[Tim5055]

There are several safety features built in to the furnace.  One of them is a "sail" switch.  Unless the fan blows hard enough to trip this switch (remember it's name, it move with the wind) the gas will not come on.  It is entirely possible that under battery poser the fan does not blow hard enough to allow the furnace to light.

Remember, if there is insufficient air flow the furnace will overheat.

Now, with that said something you said confuses me???

You said "I lit the furnace but when I tried to turn on the heat it made noise but no air hot or cold came out.".  Now, here are my questions:

1. What did you light first?

2. How did you turn on the furnace?

3.  What did the noise sound like?

On every furnace I have had, there was nothing to light.  You turned it on at the thermostat (looks like the one in the house) and set the temperature.  The noises on all mine were:

1. Fan came on for a short period of time
2. Clicking started (the lighter- 10 tries)
3. The furnace roars to life

[AZsix]

There are several safety features built in to the furnace.  One of them is a "sail" switch.  Unless the fan blows hard enough to trip this switch (remember it's name, it move with the wind) the gas will not come on.  It is entirely possible that under battery poser the fan does not blow hard enough to allow the furnace to light.

Remember, if there is insufficient air flow the furnace will overheat.

Now, with that said something you said confuses me???

You said "I lit the furnace but when I tried to turn on the heat it made noise but no air hot or cold came out.".  Now, here are my questions:

1. What did you light first?

2. How did you turn on the furnace?

3.  What did the noise sound like?

1. I have a pilot light on mine.

2. I turned the thermostat from off to on

3. It kind of a humming sound and sounded like it was going to start blowing air but nothing came out.

It could be the sail switch and the battery is not giving it enough juice to make it work.

Thanks for your reply.

[Tim5055]

1. I have a pilot light on mine.

2. I turned the thermostat from off to on

3. It kind of a humming sound and sounded like it was going to start blowing air but nothing came out.

It could be the sail switch and the battery is not giving it enough juice to make it work.

Thanks for your reply.

Yup, if there is not a sufficient force of air passing the sail switch it will never turn on.

How old is the battery?

[AZsix]

Yup, if there is not a sufficient force of air passing the sail switch it will never turn on.

How old is the battery?

I bought the battery in Sept. This is only the second time I have dry camped.

The good news is that here in AZ it will start warming up soon so I don't think I will need to use it that much. Most of the places that we camp have hook ups. It is something that I would like to get taken care of though so that I am not limited in my camping options. Maybe I need to look at getting a new charger. Maybe the one I have isn't really charging if fully.

[austinado16]

I'd suggest popping the front grill/cover off the furnace and take a look at how it's functioning with bright flashlight.

You should be able to leave the gas valve on it turned off, and use the thermostat to make it turn on the blower fan.  See what you think of how much wind it's moving....both on 12v power and on 120v power.  You could tape a strip of paper over the opening where the air exits the furnace and compare how much the paper is lifted during 12v operation, as compared to 120v operation.

If it seems like it blows significantly less on 12v, start by investigating how much voltage your battery has....both when not in use, and then when the blower kicks on.  If the battery is dipping below about 12.2v, you might have a battery with a bad cell (being that you fully charged it).

Just take it one step at a time:
1) Do I have good voltage?
2) If I have good voltage, do I have good air speed?
3) If I have good air speed, is my sail switch moving easy enough?
4) If the sail switch is moving, is it's switch actually closing so that 12v is making it over to the gas valve's magnet solenoid?
5) If 12v is getting to the gas solenoid, is the solenoid opening the valve?
6) Do these later tests with the pilot light lit and make sure the pilot stays lit.....if it doesn't you loose gas valve function

Hope this helps.

[AZsix]

I'd suggest popping the front grill/cover off the furnace and take a look at how it's functioning with bright flashlight.

You should be able to leave the gas valve on it turned off, and use the thermostat to make it turn on the blower fan.  See what you think of how much wind it's moving....both on 12v power and on 120v power.  You could tape a strip of paper over the opening where the air exits the furnace and compare how much the paper is lifted during 12v operation, as compared to 120v operation.

If it seems like it blows significantly less on 12v, start by investigating how much voltage your battery has....both when not in use, and then when the blower kicks on.  If the battery is dipping below about 12.2v, you might have a battery with a bad cell (being that you fully charged it).

Just take it one step at a time:
1) Do I have good voltage?
2) If I have good voltage, do I have good air speed?
3) If I have good air speed, is my sail switch moving easy enough?
4) If the sail switch is moving, is it's switch actually closing so that 12v is making it over to the gas valve's magnet solenoid?
5) If 12v is getting to the gas solenoid, is the solenoid opening the valve?
6) Do these later tests with the pilot light lit and make sure the pilot stays lit.....if it doesn't you loose gas valve function

Hope this helps.

It does help. I have nieghbors that have a lot of experience with TT's and I will get with them and see if we can figure out what is happening. I'm going to start with the battery. It may not be charging fully or it could have a bad cell as you suggested. With my limited knowledge it appears to be that the battery is just not giving it enough juice to work seeing how it works great when plugged in.

I'll let you know what I find out.

[waygard33]

This might be a stupid question but are you sure the pilot stayed lit? As you said, you normally camp when it is much warmer. Maybe the thermocoupler had trouble with the lower temps and would'nt keep the pilot burning?

[austinado16]

Here's a battery voltage chart that might help.  Do and archive search and see what the guys here in the know say about how low you can let the voltage drop.

I've had my furnace, probably very similar to yours with a pilot light, run fine even at no load voltages down to about 12.1v.  

You might also reach in there and see if you can spin the blower fan blades easily by hand.  Mine actually has 2 blowers.  The main big one that blows air through the furnace and into the camper, and a small enclosed blower that sucks air in from outside and feeds the burner box.

Just thinking outloud here, but you could have fan bushings that are tight, or maybe somethings hanging up (or built a nest in) the little enclosed blower area, etc.

Take it one step at a time, testing with 12v and then 120v and make everything prove that it works correctly.  You'll find the fault.

(I bought my furnace off ebay and not only was it wired up wrong, the solenoid for the pilot light flame was rusted stiff, and the gas tube for the pilot was broken.....so I had all sorts of fun getting mine working)

[AZsix]

This might be a stupid question but are you sure the pilot stayed lit? As you said, you normally camp when it is much warmer. Maybe the thermocoupler had trouble with the lower temps and would'nt keep the pilot burning?

That's what I initially thought but when I checked it, it was still burning. Then I thought that maybe I had run out of propane but somehow still had enough to keep the pilot burning. I lit the burners on the stove and let them go for a while so I knew it wasn't that.

BTW, not a stupid question. Sounds like you know me!

[austinado16]

Hey Gary, did you ever get your furnace figured out?