Its a cold one

[bill1]

Assuming you were plugged in to 110 power, I’d be sure that the converter is charging your house battery.. it sounds like the voltage dropped and
the sail switch in furnace is not being closed by the blower speed, caused by low voltage. Or if the battery was being charged and voltage was up
during the evening you could have a faulty control board.. I would suggest having the furnaces cleaned, checked, and serviced..
--
Bill and Mary Kay Boeyen
76 23' Birchaven 455
Tampa, Florida

 

[RF_Burns]

In addition to low voltage to the unit, what size propane tank are you using? If its been converter to a 20lb BBQ tank, the tank maybe be freezing up
in the cold temps. Small tanks don't have the volume to absorb heat fast enough to evaporate enough gas for the demand of the furnace.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

 

[bill1]

Could be that the drive over charged the house battery enough to get the voltage back up causing the fans speed to increase enough to let the furnaces
sail switch close letting the furnace fire up and run... again, be sure that the converter is charging the house battery when coach is plugged in..
furnace will fail once 12v drops and causes the fan speed to slow causing the sail switch to stay open. Just saying.. does not hurt to check voltage
to the house battery when plugged in..
--
Bill and Mary Kay Boeyen
76 23' Birchaven 455
Tampa, Florida

 

[Ken B]

This sure sounds like a low voltage problem slowing down the fan causing the sail switch to fail to transfer. I have never had a Suburban apart but,
if possible, lube the fan motor bearings.

Stick a voltmeter meter on the furnace and see what voltages you are dealing with when it runs correctly and compare them to when it fails.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

 

[tyler]

Don’t forget to check/address air flow too. If you stored stuff in the intake or vent paths, hose plugged or squashed kind of stuff. Easy test and
you get more heat this way as well - take the front panel off and run it with cabinet open. All heat straight out the front no distribution pipes.
--
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC

 

[Matt Colie]

> I think you guys are on to something vis the house batteries. But if Im plugged into to shore power, why would the batteries even matter?
> If the batteries are not charging from shore (and I have reason to believe they aren't) what can I do here and now?

Shane,

The house bank can be a 100% SOC, but bad connections like dirty clips holding that fuse could be the issue. If you measure the voltage at the bank
and then at the board on the heater when the fan is running, this might just tell you. Remember that the fan motor is a significant draw 6~7 amps is
not uncommon. If you have that condition just start checking connections. If you find any electrical connection that is warm, start there.

Another cheap, dirty and a little risky trick would be to buy a cheap assed battery charger and first try hooking right to the house bank. If that
doesn't get it, rig up so you can use it to power the heater board directly. The risk hear is that this cheap (not inexpensive, I mean cheap 10 Amp
charger) can and probably will make the house bank outgas. This means you will need to keep an eye on the level in the cells.

Matt
--
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit

 

[blur911sc]

> BTW Im still not understanding why the batteries matter at all if Im on shore power and all other electrical things are happy with that.

The furnace runs on 12VDC, not 120VAC, so, it runs off the batteries. Your 120VAC to 12VDC charger/converter is probably kaput and so your house
batteries aren't being charged by it.

--
Burl Vibert
Kingston, Ontario
1976 GMC 26 foot, Sheridan reno, don't know original model

 

[Ken B]

Go buy a Volt / Multimeter. They are cheap. Without one you are just guessing at the cause. You could shotgun this for weeks and not find the
cause. Get some alligator clips for it too. Do not forget that the problem could just as easily and oxidized connection on the ground side too.

https://www.harborfreight.com/11-function-digital-multimeter-with-audible-continuity-61593.html?_br_psugg_q=multimeter
Harbor Freight
Store Number 132
1301 S Brosig St.
Green Bay, WI 54311

https://www.walmart.com/ip/Hyper-Tough-Digital-Multi-meter-TD35235J/815000129
Walmart
Supercenter #1453
2440 W Mason St,
Green Bay, WI 54303

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

 

[larry nelson]

100% of the time I have had this problem in an RV it was because I was not getting proper voltage to my furnace.....100% of the time. When your
battery depletes from load, you will see your voltage at the battery go down. I had an RV whose furnace would not work at 11.9 volts. Just sayin. I am
thinking your converter is shot so it is not charging your battery. That is why your furnace is not working when the rig is "plugged in". Go get that
multimeter.....if you are not close to Harbor Freight, then go to ACe Hardware, Lowes (electrical dept), Home Depot (electrical dept). Got to be
something close to where you are. Let us know what you find.
--
Larry Nelson Springfield, MO
Ex GMC'er, then GM Busnut
now '77 Eleganza ARS WB0JOT