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Old 11-15-2010, 11:32 PM   #1
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Propane Furnace Issues when running on battery

I have a 1995 Gulfstream Scenic Cruiser Deisel Pusher. Last winter I noticed a problem that seemed intermittent at first, but I didn't bother troubleshooting until the trip we took over the weekend. The propane furnace periodically would not light when on battery power (works fine on shore power or generator). Now, it will not light on battery at all. I assumed the batteries weren't providing enough voltage, so I just replaced them (2 12V batteries in parallel). Same problem.

I'm positive I have some type of wiring issue, but cannot figure out the problem. About 6 months ago I replaced the converter, so I have a new converter as well. Here's what I have done so far:

Using a Multimeter, checked voltage at the batteries: 12.75 volt on a full charge. Check the voltage at the converter, 12.5 volts (already a loss of .25 volts on a 6 foot run with 2 gauge wire to the inverter).

Check the voltage at each of the fuse terminals on converter and reads 12.5 and check voltage on the hot lead at the furnace and it is also 12.5. Turn the thermostat on and before the fan kicks on, the voltage dips to 12.4. Once the blower motor kicks on, it dips to 10.5 then goes up to 10.9. You can hear the electric igniter clicking and you can see the spark, but nothing lights. After 3 attempts, it locks out and the blower stays running.

I had some extra 12-gauge electric wire, so I decided to run a direct run from the batteries to the furnace. I ran two ~25 foot wires through the window and hooked one up to the positive and one to the negative and connected the yellow ground wire to the negative and the red hot wire to the positive and checked the readings. The reading was 12.7 volts. Interesting enough, when the blower motor kicked on, the voltage only dropped to 12.1 volts and the electric igniter lit and everything worked great. The voltage actually seemed to climb a little the longer I let it run, which was also interesting.

So, I'm assuming I've got a bad ground or a bad wire somewhere. Since the problem occurred with the older converter and now the new converter, I'm less likely to think that is the problem. I would think I would have a lower reading when checking voltage at the furnace wire than at the converter if the wire/ground were bad, but not sure on this. I have yet to try running a direct run from the converter to the furnace. I'm just trying to figure out if I'm missing something completely obvious here. What about the .25 volt drop on 2 gauge wire on a short 6 foot run from the batteries to the converter?? All other appliances work just fine.

Any help or insight would be much appreciated!
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Old 11-16-2010, 12:34 AM   #2
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Well, your right at that age where corrosion starts to become a problem. The drop to 10v is a concern and would support your conclusion of a bad connection/corrosion. Look around and make sure someone hasn't spliced in with an unprotected wire nut too..

Did you say that the furnace lit off and ran when directly wired?
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Old 11-16-2010, 03:23 AM   #3
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Since you have a fully charged battery bank (12.75vdc) your converter does not need to charge and therefore is only maintaining (12.5 vdc). Drain off some of the battery voltage and check the actual charging voltage of the converter to determine if there is a problem with it. You probably do have loose connections and the frame ground would be one of the first things I would check. If you find that you have a bad ground to the furnace, just run a new one. Good luck and keep us posted.
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Old 11-16-2010, 07:59 AM   #4
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Originally Posted by Midniteoyl View Post
Well, your right at that age where corrosion starts to become a problem. The drop to 10v is a concern and would support your conclusion of a bad connection/corrosion. Look around and make sure someone hasn't spliced in with an unprotected wire nut too..

Did you say that the furnace lit off and ran when directly wired?
Yes, when directly wired, the furnace works just fine and the voltage stays up there. When I reconnect the original wiring, that is when I see the drastic voltage drop and the electronic ignition fails to light; though it does spark and you and hear the sparking sound and you can see the spark. The one thing that keeps baffling me is why everything works fine when on shore power or generator. I would think since it is a DC system getting fed through the converter, everything is going through the same wiring; if I had a bad wire, ground problem or corrosion, wouldn't the problem present itself all the time?
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Old 11-16-2010, 08:29 AM   #5
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Just so we are talking about the same thing here......The propane furnaces do not run off the converter they run directly off the battery and the charger/converter connects to the battery. What you are saying is correct in a very roundabout way that there is a difference. The propane furnace is a 100% 12 volt system and that is why it is wired to the battery. You know that the ignitor is working because you can hear it and it still will not light means that either a safety interlock has shut off the gas supply solenoid in the furnace or the gas supply solenoid is bad or has a bad connection. The other item that is in the circuit is the emegency shutoff solenoid hooked to your gas detector. If this is malfunctioning then it shuts off all the gas.

There are numerous safety interlocks in a furnace and the most common problem is the flapper valve. There is a air flapper valve in the furnace that opens when the fan starts up to vent out and old gas. If a mud dauber has built a nest on the flapper valve then it is too heavy to open all the way and will not allow the gas to turn on. If the unit is just on the battery without the charger being on then it might be that the fan is just not blowing enough to move this flapper to activate this switch then when the converter is on more voltage is supplied to the battery wihich makes the fan run a little harder so it activates the switch. This is a real common problem and makes sense given everything that has been said.
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Old 11-16-2010, 08:45 AM   #6
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did you ck voltage at the battres with the furnace trying to run ? since it works ok with shore power or gen set that would elimanate much of the wiring and connections if you have 12.5v at the battres under load i would connect a volt meter at B- on the battery to B- at furnace any voltage with furnace trying to run indicates bad wire or connection same goes for B+ good luck lee
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Old 11-16-2010, 09:05 AM   #7
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Here's my theory.
When the furnace is running off battery power only (@12.7 volts), the bad connection or whatever is enough to drop the voltage below what is required for the furnace to operate properly.
When operating off shore power or generator the converter is probably putting at least 13.4+ volts on the batteries in order to keep them charged. This increase in voltage will now be also seen at the furnace and is enough for proper operation of the furnace.
Sounds like a poor connection somewhere.
That's my two cents worth anyway.
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Old 11-16-2010, 09:14 AM   #8
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I seriously doubt that there is a bad connection. If it works once then it works. These 12 volt appliances work all the way down to 11 volts and sometimes a little lower. This is such a common problem at this time of the year with mud daubers building a nest in or on a furnace. Take off the outside grill to the furnace and get a flashlight and look in or stick your hand in there and knock of the nest. Then keep watch ing from outside with a flashlight and watch and see if that air flapper valve openes all the way when the fan turns on at the beginning of the cycle.
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Old 11-16-2010, 11:11 AM   #9
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I am making headway. Tell me your thoughts on this. I thought the voltage drop at the converter was interesting. I decided to take the 6 gauge hot and ground wire off the converter and test the voltage. When I go out to the batteries and check voltage this morning (after unplugging from shore power and leaving them unplugged for a bit); the voltage was 12.85. I checked the voltage from the two wires at the converter (while disconnected from the converter) and voltage is 12.45. Since I already have my long 12-gauge wires that I was using to go directly to the batteries, I decided to wirenut these to the wires that feed the converter. Turn on the furnace and the voltage drops to 10.8 as soon as the fan comes on, then climbs to 10.95 after the fan has fun for a few, electric spark tries to ignite, no ignition, low voltage is my guess. Something is causing a loss in voltage from the batteries to the wires that feed that converter.

Just to be sure it is voltage, I took my wires back out to the battery posts and tested again and everything works fine and the voltage only drops about .5 volts, when connected directly to the batteries.

Now comes the challenge. I thought cables from the batteries went straight to the converter. However, they are 2-gauge (really thick) cables. In following the cables, the ground goes straight to the chassis. The positive goes to something that is mounted to the chassis where other 2-gauge cables are connected. From there, it looks like the Positive cables go elsewhere. SOMEWHERE along the long, there is a splice because the cables coming into the converter are 6-gauge cables.

Would there be an issue with me either running a hot and ground cable straight from the battery compartment to the converter? The battery compartment is almost right under the bed where the converter is. I would think it would be pretty simple and shouldn't be more than 6 feet of each cable. Any clue where these 6-gauge cables come from or are getting spliced in? I wish Gulfstream would provide a schematic.

Thanks all! I feel I am close to getting this issue fixed!

Chris
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Old 11-16-2010, 07:23 PM   #10
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Ok.. while the igniter can work down to about 10.5v, the fan really needs more than 11.5v to maintain the proper speed to trip the 'sail switch'. No sail switch, no propane.

Chris: I too wish I had a wiring schematic . However, your on the right track. I'm betting on some type of crimped clamp thats corroded.
Quote:
The positive goes to something that is mounted to the chassis where other 2-gauge cables are connected.
Where is this? Power Distribution Center? Mines all the way up on the firewall.
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Old 11-16-2010, 07:25 PM   #11
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Originally Posted by Mike Canter View Post
I seriously doubt that there is a bad connection. If it works once then it works. These 12 volt appliances work all the way down to 11 volts and sometimes a little lower. This is such a common problem at this time of the year with mud daubers building a nest in or on a furnace. Take off the outside grill to the furnace and get a flashlight and look in or stick your hand in there and knock of the nest. Then keep watch ing from outside with a flashlight and watch and see if that air flapper valve openes all the way when the fan turns on at the beginning of the cycle.
If it works good directly wired, but doesnt when using the coaches wiring, along with the difference in voltage drops he recorded between the two ways, how could it be mud daubers?
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Old 11-16-2010, 07:26 PM   #12
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Originally Posted by Richardrky View Post
Here's my theory.
When the furnace is running off battery power only (@12.7 volts), the bad connection or whatever is enough to drop the voltage below what is required for the furnace to operate properly.
When operating off shore power or generator the converter is probably putting at least 13.4+ volts on the batteries in order to keep them charged. This increase in voltage will now be also seen at the furnace and is enough for proper operation of the furnace.
Sounds like a poor connection somewhere.
That's my two cents worth anyway.
Agree...
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Old 11-16-2010, 07:50 PM   #13
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Jim, there is a certain voltage drop in wires over distance and this voltage drop is accepted because nothing in a 12 volt analog appliance is very voltage critical. If the mud dauber made a nest on the outside of the sail/flap then it has increased the weight of the sail/flap so the voltage that is dropping a little and coming through the coach wiring is not allowing the DC voltage fan to blow enough to move the heavier sail/flap to actuate the switch. When the wires are run directly and a little higher voltage is applied to the DC fan then the fan blows a little faster and harder and can now move the heavier sail/flap enough so it hits the switch and the furnace gets gas and it all works.

Like I said this is not super sophisticated digital computer that needs accurate voltage to work. Analog DC appliances don't care if it is 10.5, 11.9 volts or 12.3 volts or 12.9 volts. The window for voltage is very wide.

Lets stop and think for a moment. When the furnace is turned on the fan is on and you can here the ignitor going so it has the correct voltages to work that far. The only thing that is really not happening is that the gas is not turning on and that has to be because of the sail switch is not being turned on because it cannot move enough to hit the switch.
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Old 11-16-2010, 10:09 PM   #14
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Lets stop and think for a moment. When the furnace is turned on the fan is on and you can here the ignitor going so it has the correct voltages to work that far. The only thing that is really not happening is that the gas is not turning on and that has to be because of the sail switch is not being turned on because it cannot move enough to hit the switch.
I gotcha Mike..and it maybe it is, but dont forget that it runs fine directly wired. It also was intermittent last season, and works fine on shore or generator power...Its not like he has only a .5v drop.

As a part of this, I was looking through the paper work that came with my coach just this last weekend and ran across a couple of emails from a tech discussing just this issue with the previous owner. The voltages I stated above came from them.


edit: I just looked at it again, and my post above.. I made a mistake...; Its the Gas Valve that requires at least 10.5vdc to operate, not the igniter... My apologies. However, the problem is still voltage related.

(sorry.. kinda distracted at the moment...)
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