Suburban furnace dead

[Beauty & the Beast]

Went camping last weekend and had no heat!
2019 momentum 376th
When i put on heat and in auto i get nothing but error message on the lci screen under central unit (i wish there was a separate thermostat for this) so turned on stove burners to make sure i had gas flow to purge any air, pulled cover to make sure switch was in on position and tried again nothing, so ran fireplace for the 2 day's
when I got home did some research and testing and still not working
2 blue wires thermostat i believe 1 red power 1 yellow neutral
So when I pulled furnace out and test wires I get 9volts is that normal i thought it needs 12 volts
Tested sensor on the back for continuity it's good, called GD they said replace board
it's a SF-35Q looks like it has never been used no discoloration board and all components r perfect
bought rv from older couple in Florida that hardly used it and probably never used the heat
Furnace is on my bench, please give me some ideas/test before I start buying parts
Thanks in advance for any help

[ncitro]

Went camping last weekend and had no heat!
2019 momentum 376th
When i put on heat and in auto i get nothing but error message on the lci screen under central unit (i wish there was a separate thermostat for this) so turned on stove burners to make sure i had gas flow to purge any air, pulled cover to make sure switch was in on position and tried again nothing, so ran fireplace for the 2 day's
when I got home did some research and testing and still not working
2 blue wires thermostat i believe 1 red power 1 yellow neutral
So when I pulled furnace out and test wires I get 9volts is that normal i thought it needs 12 volts
Tested sensor on the back for continuity it's good, called GD they said replace board
it's a SF-35Q looks like it has never been used no discoloration board and all components r perfect
bought rv from older couple in Florida that hardly used it and probably never used the heat
Furnace is on my bench, please give me some ideas/test before I start buying parts
Thanks in advance for any help

I would replace the board. Dinosaur makes a nice replacement I have had really good luck with in refrigerators, water heaters and furnaces. You can get it on Amazon Prime, and easy returning if that does not fix it, but I would put good money on it being the board.

[howson]

Thanks in advance for any help

Check out this thread: https://gdrvowners.com/forum/operati...roubleshooting

[Beauty & the Beast]

Almost forgot I can spin fan so that is good and I cracked the gas line nut loose and yes it was getting gas for sure stinky
I will look for the dinosaur 🦕 board

[TucsonJim]

Since it's not firing up, the high limit switch is likely not the issue.
And just to confirm... The blower motor is not turning on either right? If not, it rules out the sail switch.

If you have good battery voltage, then the control board is the most likely culprit.

Jim

[Beauty & the Beast]

Check out this thread: https://gdrvowners.com/forum/operati...roubleshooting

Good find i did see that video but forgot to watch i will inspect sail switch
just for the record the furnace in my rig is very easy to remove 4 wires gas line and 1 screw
slides in like butter no duct work to remove 👍

[Beauty & the Beast]

I would assume the thermostats r good since we used all 3 ac units this past summer and they worked flawlessly

[Brian S]

Before you start looking at the sail switch, remember that it is activated by the fan. The same motor is used for the burner and the circulating fan. The fan starts to run as soon as the thermostat switch makes. The 9 volts you are getting is concerning. Can you measure the voltage at the furnace before and after it tries to start. If it is 12.6 or better before, you know you have proper voltage. If your rig is plugged in to power, the voltage will be 13 or higher. If when the thermostat switch closes, and the voltage drops real low like 9 volts, something is pulling it down such as a bad motor or faulty board. If possible, carefully (watch your fingers!) try spinning the fan while it is trying to start.

[Beauty & the Beast]

First it doesn't try to start no noise nothing
the furnace is on my bench in barn so the red power and yellow ground is showing 9 volt connected to nothing and im connected to 30amp service that i have been using for the past 5yrs so somewhere im losing voltage
my meter should be 12/13 volts
on lci screen monitor panel shows battery at about 13.1 so im losing voltage somewhere on its way to furnace

[Beauty & the Beast]

Following that red wire is going to be a pita 👎

[Brian S]

Yes, can you check it at the fuse or breaker on your electrical panel to see if you have full voltage on that circuit?

[Beauty & the Beast]

Yes that was my plan
I do electrical work on side jobs but I'm not an rv expert so the power comes in and goes to main panel then to 12volt converter?

[howson]

Yes that was my plan
I do electrical work on side jobs but I'm not an rv expert so the power comes in and goes to main panel then to 12volt converter?

Yes.

There should be a circuit breaker associated with the converter. Turn the converter c/b off so you're running off of just the battery (or just shut off shore power)--what is the voltage at the furnace wires?

[Brian S]

Yes, the converter takes in the 110 volts A.C. and converts (or inverts) to 12 volts DC. A full 12 volt battery is 12.6 volts or higher and the converter creates a charging voltage of 13 - 13.5 volts DC. If you only have 12 volts to the furnace, I suspect it comes off a small blue 15 amp plug in automotive fuse. If you could take a battery into your shop and power it directly, that would eliminate any issue with the electrical wiring. Whenever i have to pull my furnace out, it is usually because it has an insect nest or blockage in the gas orifice. It is a pain and I cannot easily hook up a propane line on the bench to fire it, but I can take a battery out of my boat and at least run it through its cycle and check for good spark and fan operation.

[Brian S]

I do not recommend trying to run the furnace off of a battery charger!