Suburban SF-30FQ Furnace Questions

charlie46 · 01-29-2021, 03:11 PM

Hi All. I have a mystery for the group. I have a 2013 290 SRE Laredo that we full time in on a construction site. A few weeks ago, we had a 125 gal propane tank installed. The large tank has a regulator installed but it reduces the line pressure to 14psi going in to the changeover regulator. The indicator is always red when the the switch is thrown to the large tank. For the two onboard bottles, both have line pressure of roughly 60psi and the indicator is green when switched to these bottles. My first questions involve the regulators. Is the large tank using the correct regulator? Could it be set up for a residence rather than an RV needing slightly higher pressure than a house?

After going through about 40 gallons off the large tank, my furnace died. It is a Suburban SF-30FQ. Actually quite easy to remove and replace. Cold, the heat sensor shows 0 across the terminals. I assume this means the sensor is open. I did find two mummified mice inside the furnace. They died warm, but more importantly, they died. Cleaned them out and popped open the blower housing. It was a bit dusty and the sail switch had some lint in it blocking some function. Cleaned all that up, reassembled the unit, reinstalled it, and fired it up.

It worked flawlessly for about an hour, then died. The 15amp fuse was blown. Attempting to replace the fuse, with the thermostat dialed all the way down and the heat switch turned off, the fuse arced and blew as I attempted to replace it. The thermostat does not click now nor does the ignitor, obviously because there is no fuse. With everything off, I have 13.65V across the fuse terminals.

Everything else in the trailer works fine. I am going to pull the furnace again to look at the circuit board. I will say that Suburban has done a great job of posting their manuals online. Before I start throwing new parts at it, is there anything else I should be checking?

Thanks in advance.

Paul

jasin1 · 01-29-2021, 03:49 PM

Quote:

Originally Posted by charlie46

Hi All. I have a mystery for the group. I have a 2013 290 SRE Laredo that we full time in on a construction site. A few weeks ago, we had a 125 gal propane tank installed. The large tank has a regulator installed but it reduces the line pressure to 14psi going in to the changeover regulator. The indicator is always red when the the switch is thrown to the large tank. For the two onboard bottles, both have line pressure of roughly 60psi and the indicator is green when switched to these bottles. My first questions involve the regulators. Is the large tank using the correct regulator? Could it be set up for a residence rather than an RV needing slightly higher pressure than a house?

After going through about 40 gallons off the large tank, my furnace died. It is a Suburban SF-30FQ. Actually quite easy to remove and replace. Cold, the heat sensor shows 0 across the terminals. I assume this means the sensor is open. I did find two mummified mice inside the furnace. They died warm, but more importantly, they died. Cleaned them out and popped open the blower housing. It was a bit dusty and the sail switch had some lint in it blocking some function. Cleaned all that up, reassembled the unit, reinstalled it, and fired it up.

It worked flawlessly for about an hour, then died. The 15amp fuse was blown. Attempting to replace the fuse, with the thermostat dialed all the way down and the heat switch turned off, the fuse arced and blew as I attempted to replace it. The thermostat does not click now nor does the ignitor, obviously because there is no fuse. With everything off, I have 13.65V across the fuse terminals.

Everything else in the trailer works fine. I am going to pull the furnace again to look at the circuit board. I will say that Suburban has done a great job of posting their manuals online. Before I start throwing new parts at it, is there anything else I should be checking?

Thanks in advance.

Paul

Did the mice chew up any wires? That could be shorting out and causing the fuse to blow. And the gas pressure should be the same for home or rv

**JRTJH** · 01-29-2021, 06:44 PM

The gas pressure at the furnace manifold should be 11" water column.

If your RV has a "red or black" intermediary regulator on the "off regulator side" it is probably a 30PSI regulator. That prevents "liquid propane from being in the crossover pipe. The automatic changeover regulator senses "above 30PSI" and will switch to the opposite (full) tank when gas pressure falls below that value. Apparently, your "big tank intermediary regulator" (which does the same thing as the 30PSI regulator <prevents liquid propane from flowing into the crossover pipes>) is set below the "changeover value of your automatic changeover regulator"... So, even with a full 250 gallons, the 14 PSI pressure arriving at your automatic changeover regulator sensing device is not enough to keep it from "tripping to the other tank" and is causing it to believe that it is sensing an empty tank and causing it to switche to the other (that gives you the "red/empty" indicator in the regulator window.

I'd suppose that if you're only getting 14PSI into the regulator, it's having issues providing the 11'wc at sufficient volume (not pressure) to maintain the amount of cubic inches of gas into the furnace blower (probably 35,000BTU).

So, the furnace would not operate, likely "tripped off" several times, blew the fuse and now, is either locked up and will continue to blow the fuses or has damaged the control board.

My first recommendation would be to operate the trailer on the original propane tanks (30 pound ones) to rule out a propane pressure issue, then disconnect the battery from the trailer, unplug the shore power, turn the thermostat to OFF and with the trailer in a "NO POWER" condition, let it sit for about 5 minutes. Then reconnect the battery, plug in shore power and reinstall a fuse. Then turn on the thermostat and see what happens. If it continues to blow the fuse, I'd do a thorough check for damaged wires within the furnace and from the fuse panel to the furnace.

Keystone uses "lowest bid wiring" which is typically insulated with plastic manufactured from soy oil. Yes, SOY OIL, which, in the real world, is "mouse food" so it's no surprise that mice tend to gnaw on cheap wire insulation.....

And now you know, "the rest of the story"...

To condense the above, see if you can "reset the furnace/thermostat by removing all power, then with a "known good propane source, power up the trailer and see what happens. If it still blows the fuse, then check all the wiring carefully, if the wiring is good, I'd suspect the control board in the furnace.

But,

charlie46 · 01-30-2021, 09:30 AM

The transfer switch is not automatic. It is a manual throw from tank to tank. I'm thinking the regulator on new tank is stepping down the pressure before it reaches the RV regulator and might be starving the furnace for gas volume, though the stove and water heater work fine. The flame on the stove is mostly blue with occasional flickers of yellow, reinforcing the thought that the double regulators may be starving the system. The weather is decent here today so will be disconnecting the power as you described. If that fails to reset the furnace I'll be pulling the unit and doing more than just cleaning the blower wheel and sail switch. I found a refresh kit online and a dinosaur circuit board but won't through parts at it until a more thorough examination.

charlie46 · 01-30-2021, 09:32 AM

A second thought. Should the large propane tank be plumbed in to the RV system before (upstream) of the RV regulator? Or should it be plumbed in after (downstream) of the RV regulator to prevent the double-regulation?

charlie46 · 01-30-2021, 09:33 AM

And no one commented on the trailer or the towing unit, so I am assuming I'm legal.

**JRTJH** · 01-30-2021, 10:27 AM

Quote:

Originally Posted by charlie46

And no one commented on the trailer or the towing unit, so I am assuming I'm legal.

The fact that nobody commented on the trailer or truck is NOT a signal that nothing is wrong.... Hopefully you were just allowing a bit of sarcasm to escape your keyboard.... We do have some members who "get headaches" if someone mentions weight in a post while most are not bashful to comment on a safety related item when it's appropriate. If you're asking about the appropriateness of your rig's weight status, post the information and you'll surely get as much "unfiltered advice" from both sides of the spectrum. Some saying "hell, you're OK, I do it all the time, so just go play" and some saying "Here's the numbers and how they stack up in your specific situation".

travelin texans · 01-30-2021, 10:28 AM

Quote:

Originally Posted by charlie46

A second thought. Should the large propane tank be plumbed in to the RV system before (upstream) of the RV regulator? Or should it be plumbed in after (downstream) of the RV regulator to prevent the double-regulation?

If the big tank has it's own regulator it will need to be plumbed in downstream of the rv regulators otherwise it's double regulated & would be lucky to get a small flame on one burner of the stove top. Or remove the regulator from the big bottle then tie in upstream of the rv regulator.
This would be like connecting your grill to the provided rv disconnect, if the grill has it's own regulator it must be removed or you'll get very little flame, if any, on the grill.

charlie46 · 01-30-2021, 10:49 AM

It WAS just a touch of sarcasm. I had seen an earlier post about poop pyramids that turned in to a flame war because the towing unit was much smaller than it needed to be for the trailer. All the "experts" weighed in (bad pun) on the truck/trailer combo rather than his initial question.

**JRTJH** · 01-30-2021, 10:52 AM

Quote:

Originally Posted by travelin texans

If the big tank has it's own regulator it will need to be plumbed in downstream of the rv regulators otherwise it's double regulated & would be lucky to get a small flame on one burner of the stove top. Or remove the regulator from the big bottle then tie in upstream of the rv regulator.
This would be like connecting your grill to the provided rv disconnect, if the grill has it's own regulator it must be removed or you'll get very little flame, if any, on the grill.

What Danny said is spot on..... With the additional comments that "PROVIDED your big tank regulator" output is 11"WC... If it's an "intermediary regulator" designed to step down the pressure which is "further reduced by the primary regulator" then if you remove the "primary regulator" you may apply 14PSI to your furnace and "blow it up"....

So, take stock of YOUR propane connections and assure that what finally gets to the gas appliances is regulated at 11"WC. Any "other pressure from multiple regulators may or may not be causing an issue"...

Danny is right, you can't "double regulate your propane source with two final regulators" and have a satisfactory output to the appliances. You also can't remove or bypass the regulator that's producing 11"WC and use, in its place, one on the "big tank" that's producing 14PSI....

Check YOUR system as none of us are able to decipher how it's actually connected to YOUR trailer gas supply system.

jasin1 · 01-30-2021, 10:53 AM

Kind of a confrontational way to start out on the forum.....just sayin
See post #9 above... never mind I see you’ve been here awhile

**JRTJH** · 01-30-2021, 10:56 AM

Quote:

Originally Posted by charlie46

It WAS just a touch of sarcasm. I had seen an earlier post about poop pyramids that turned in to a flame war because the towing unit was much smaller than it needed to be for the trailer. All the "experts" weighed in (bad pun) on the truck/trailer combo rather than his initial question.

Well, your comments can be viewed as either "sarcasm" or "rubbing salt in other people's wounds"... Neither is a really congenial way to seek help for an unrelated situation....

charlie46 · 01-30-2021, 01:52 PM

LOL. I'm pretty sure I'm legal, at least as far as weights, rigs, and tires go. The Sarcasm Police would see me hung.

charlie46 · 01-30-2021, 02:07 PM

Here's the tank, the "octopus" gas valve, and the scorched circuit board.

jasin1 · 01-30-2021, 02:28 PM

Quote:

Originally Posted by charlie46

Here's the tank, the "octopus" gas valve, and the scorched circuit board.

It’s probably been mentioned before but if that large tank regulator is showing 14” wc after the regulator and you try and hook it up before the rv regulator it probably is not allowing the rv regulator to open. It needs to see a much higher input pressure ( tank pressure) If you want to use it I needs to be on the other side of the rv regulator. Bypassing it altogether then set the big tank regulator to 11” wc
The board issue is unrelated to gas pressure issue

jasin1 · 01-30-2021, 02:31 PM

Yes sorry it’s been mentioned several times lol
As a side note as long as the large tank regulator is adjustable down to 11” then I would use that so you don’t have a rubber hose 10’long with high pressure propane going across the lawn to your little tiny rv regulator

jasin1 · 01-30-2021, 02:43 PM

Also you said the fuse arced and blew when you tried to replace it. Was the board powered up when you tried that? Wondering if you used needle nose pliers or something like that and it shorted to furnace cabinet and I’ve seen worse looking boards that still worked. Is that black spot the opposite of the fuse? The solder joints for the fuse holder? If so it may have a hotspot from being loose after fuses were roughly installed in the past

charlie46 · 01-30-2021, 04:58 PM

Quote:

Originally Posted by jasin1

It’s probably been mentioned before but if that large tank regulator is showing 14” wc after the regulator and you try and hook it up before the rv regulator it probably is not allowing the rv regulator to open. It needs to see a much higher input pressure ( tank pressure) If you want to use it I needs to be on the other side of the rv regulator. Bypassing it altogether then set the big tank regulator to 11” wc
The board issue is unrelated to gas pressure issue

The line coming from the large tank showed 14psi. That is 387wc so I'm not thinking I want to feed that directly into my fuel system. I'll have a conversation with the installer on Monday. Good point about the hose. One doesn't tend tink about UV damage in January.

jasin1 · 01-30-2021, 05:01 PM

Quote:

Originally Posted by charlie46

The line coming from the large tank showed 14psi. That is 387wc so I'm not thinking I want to feed that directly into my fuel system. I'll have a conversation with the installer on Monday. Good point about the hose. One doesn't tend tink about UV damage in January.

Wow my mistake I misread and thought you were saying 14”wc lol
I was wondering why John in an earlier post in this thread was concerned about 11”wc vs 14” wc it was 14psi. I need to read more thoroughly

charlie46 · 01-30-2021, 05:14 PM

Quote:

Originally Posted by jasin1

Also you said the fuse arced and blew when you tried to replace it. Was the board powered up when you tried that? Wondering if you used needle nose pliers or something like that and it shorted to furnace cabinet and I’ve seen worse looking boards that still worked. Is that black spot the opposite of the fuse? The solder joints for the fuse holder? If so it may have a hotspot from being loose after fuses were roughly installed in the past

The picture of the circuit board is not the fuse block. The fuse that kept blowing was in the fuse panel on the side of the sink. The temperature was set at the lowest setting and the heat was turned off. I was using a non-conducting fuse fuller to in stall the fuse. It should not have had power. I pulled the furnace unit and cut the wires. I installed a new 15A fuse with no issues. With the thermostat settings as previously describe (low temp and heat off) the feed wires showed 13.65V and the fuse didn't short, suggesting the short is in the furnace. Close examination revealed no rodent damage to the wiring on the furnace. The circuit board was scorched at the Power In pin where it feeds into the Zettler relay. I am assuming the relay is shorted and will confirm with destructive testing. I am further assuming low propane flow may be causing more frequent cycling (another commenter posited that low propane flow causes a lean condition, hotter burning, and more frequent cycles of the limit switch and circuit board relay(s?). Parts on order with one of those dinosaur upgraded circuit boards.

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