Propane furnace won't turn on

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Smoky

Smoky

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Joined
Mar 11, 2005
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Last night our furnace would not turn on.

We have plenty of propane and all our other propane systems are working fine.  Fortunately we carry a small electric heater so it kept the bedroom warm.  And now this morning at 6 am I am running the forward heat pump in the salon area.

I checked the furnace fuse in the bathroom and it is good.

I am looking for troubleshooting tips.  I have a subruban SF-42 gas furnace.

Smoky
 
Sorry guys I was not more complete.  Was early and I was freezing LOL!  :)

Absolutely nothing seems to happen.  No fan kicks on and no sign of heat.  laster on today going to have the Admiral turn up the thermostat while I stand outside and watch and listen.

In the meantime is there any way to test if the main blower is still functional?

I had a problem earlier this year with the auxiliary blower in the basement at the utility bay.  Discovered with the help of the forum that there is a 5 amp fuse for it under the fridge behind the floor panel.  Replacing the fuse got it working.  The fuse is still good, but the aux blower doesn't go either.  I think it is wired to go on when the main blower goes on.  or it can be taken out of the circuit by shutting off a switch at the utility bay panel.  I have it shut off right now.  Main blower does not run either way the aux switch is set.

There is a 20 amp fuse for the main blower located in the bathroom.  It is good.

Wonder if there are voltage checks I could be making?

Are there any safety overrides to keep the furnace from coming on and if so, what variables activate the overrides?

Smoky
 
Just downloaded Gary's trouble shooting guide and it is terrific!  Will take me some time to work with this.  I just a minute ago tried a reset using the thermostat.  No luck there.

I also now remember that a few days ago I noticed that there was no longer a delay when I turned the furnace on.  The blower would go on immediately and the warmth would arrive in a couple of minutes.  There was still a delay when I turned furnace off so the blower was properly cooling things down.  The air conditioner has a start up delay as does the heat pump.  But the furnace blower starts now without a delay.  At least it did before this morning.  I think I recall the blower used to wait a few second before coming on.  Now nothing seems to start.

Will report back later after I go into town and then get the Admiral to assist me when I come back this afternoon.

Ain't RVs fun?  :)

Smoky

 
The blower has to come on before the furnace will light.  No delay is probably what you should expect.  There is a sail switch that must be closed by the air flow or gas will not come on.  Since your blower is not coming on, nothing else will happen.  Fix the blower problem and you'll probably have heat.
 
OK Tom & Joyce, thanks a lot!

Well I brought some contact cleaner spray home and some air spray.  But too late now to do any more testing.  This discussion is pointing more and more to an electric circuit problem.  Usually these are solved by finding burnt fuses.  So far not the case.  So I will go over everything and try to be sure all contact points are clean and working.

If that does not help, I wonder what I will do next.  Maybe there is some way to apply direct voltage to the blower circuit?

Guess I will be working on this a few more days.  Need to take time to read Gary's trouble shooting guide in detail.  I hope we get this fixed soon as it will be a Quartzite trip stopper if it isn't fixed by the 23rd!  :mad:

Unless it is my turn once again for the 30 amp or 50 amp power post at Tyson's Wash!!  ;D

Smoky
 
Unless it is my turn once again for the 30 amp or 50 amp power post at Tyson's Wash!! 
grin.gif
Click to expand...

Sorry Smoky, I left ours home and Ron's isn't going to be there either. :(
 
Smoky said:
Maybe there is some way to apply direct voltage to the blower circuit?
Click to expand...
A possible monkey wrench in that thought is just where and how you might apply voltage to the blower.  The reason for no fan will likely cause no ignition as well.  Jumping to the blower may or may not apply power to the control board as well.  Can you tell if there is 12v to the thermostat?
 
One way to test the furnace starting is to apply 12V to the "W" lead at the thermostat after disconnecting it from the thermostat. proving whether the thermostat or furnace is the troublemaker. You will likely have to take the cover off or dismount the thermostat to gain access to these leads. Both 12V (which powers the thermostat) and the "W" lead are available there. This should start the furnace blower.

If it does not, I would try and find a fuse for the furnaces 12V supply itself. (I'm voting for this as the issue!!) You could check at the furnace using a voltmeter for the presence or absence of 12V.  (The coach/trailer wiring is all connected to the furnace, likely with wire nuts, next to the furnace, a convenient spot to open/test). As mentioned previously, nothing will happen unless the fan is running at full speed. When you get that working, after a short delay, you should hear the furnace try to ignite (clicking sound -"sparking"), When it does, the clicking  should be replaced by a low "roar".  Note: With an electronic thermostat, after setting the temperature, there is usually a short delay before anything (heat or air) kicks in. Listen for a small click from the thermostat relays.

I hope yours has a better access than my SF42. I had to remove the stove and open a wooden box underneath it, no access from outside!!!!

Good luck!!!
 
Good news. The furnace is running again.

I found a very weird situation.

I kept examining the 3 fuses related to this and they were all coming up good.  Finally today, out of desperation, I decided I would replace each fuse even if it looked good.

I tried the 20 amp fuse first, since it was in the main blower circuit.  Voil?.  The blower came on and the furnace worked.  I looked at the dang fuse (old one) and it looked good as new.  I put it in another circuit and sure enough the other circuit did not work.  Has anyone ever run into this before?  A fuse that looks good but won't work?  I got out my multimeter and sure enough there was no continuity.

Oh well.  A lot of wasted time, but nothing more than a fuse.

Thanks to everyone for their help.  I learned a lot and especially like Gary's troubleshooting guide.

See you all at QZ!!

Smoky
 
Smoky said:
A fuse that looks good but won't work?
Click to expand...
This is not too uncommon.  Fuses have to have a connection at either end and sometimes the spot weld or solder joint is bad.  Fuses that fail in this way do so due to a defect.  Fuses that open in the middle where you can see it do so due to excessive current (did its job).

I'm glad you got er fixed.
 
Smoky,

This is a learning moment.  Whenever there is a no operation situation and you check the fuses, ALWAYS measure the voltage across them or measure the continuity before believing them good.  No voltage across the fuse generally indicates they are good IF voltage is present and continuity is also generally a good indicator. 

Nothing is absolute so I am protecting myself with the "generally" comment as I have seen some strange situations with fuses. 
 
Thanks Jim.

I am calling it a "re-learning" moment as I should have done that. I only posted the ending of the story because I didn't want my embarrassment to leave others wondering (and maybe learning)  :)

I got going down the wrong track because I woke up cold and shivering the first morning and tried to find a quick fix.  Then things went down may roads from there LOL!

Also I love the many interesting observations people make as they aid on solving a problem.

How did we ever manage 30 years ago when it was just me and the dealer expert and no friendly knowledgable peers across an electronic network to compare notes with?

Smoky

 
I like to ask about a propane furnace also. I am just leaving Minnesota in a borrowed conversion van. The owner just bought it last fall and only had it out two times. She said the furnace worked fine. I tried it before I left, the furnace comes on blower and all. At first it felt like it was starting to warm up, so I let it run for a half hour. Came out to check it and no heat, just cold air and a faint smell of gas. So turned all off, aired it out and tried again. But no heat. It is very cold here and I was woundering if it wouldn't heat because of low pressure, or moisture in the pilot that froze, so I tried the stove and that worked fine. I figured I would try again when I got to warmer weather. Also can anyone tell me about the refrigerator, it is gas or 12V. I did not try the gas part but while it was plugged in to AC I tried the 12V and it did not seem to work. I didn't test fuses it is just too cold. I hope to know a lot more about this Van and its operation than the owner does otherwise this will be a sorry trip. Mud Puppy
 
Smoky,

A fuse tester is what you need.  With a fuse tester, you can test fuses without even removing them from the fuse holder.  You simply press the two metal probes at one end of the fuse tester into the end of the fuse and a green light tells you if they are good or not.  With the Buss fuse tester that I have, you can check 3 sizes of fuses, MAXI, ATC, and ATM.  When you are checking a whole bank of fuses, this will save you a lot of time and agony (sometimes you break fuses just by extracting and re-inserting them).  It's fast and easy and non-invasive.  See pictures below.
 

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