Suburban furnace problem. Troubleshooting procedure?

[showme]

We have a 2000 Montana 5th wheel that we keep down at our property. We mainly use it for a break room and to keep tools in until we build a house there. We bought the 5th wheel 2 years ago for this purpose, and before we took it down to the land, we had it gone over by a local rv shop (now closed due to retirement), and every thing worked fine. This week I replaced a piece of flex duct running to the bedroom, and since it's getting cold I thought I'd fire up the furnace (a Suburban SF-35F, s.n.000705372) just to make sure it works if we need it. (We used the ac when we needed to take a break from clearing brush often this summer, with the generator).
Anyway, after checking to make sure we didn't have any mice nests in and around it (it's out in the country in the middle of 43 acres of woods), I tried it, but no luck. Checked the battery, and it was too low, so I put a good battery in. The digital thermostat came on, and I turned the heat up to 76 to blow the system out, leaving the lp off. No fan, no nothing. I checked the fuse and it's ok. I went ahead and turned the gas on just in case I was thinking backwards, but that didn't help either. So, the thermostat lights up, and lets me switch hi/low fan, adjust the temp, but no fan, no click, no nothing. The battery was showing 12 volts when I metered it. My question is, what is the procedure to troubleshoot this OR what is the first thing you all would consider checking. Since I have no schematics for this trailer, and the wiring is pretty non-descript, I'm having a heck of a time figuring out how to trace the wiring. Also, this rig doesn't have an outside access to the furnace and it's crammed under the sink. How the heck do you even get in there to check anything out? I took the 'front' (inside) faceplate off to check the burner area, but I have no idea how a person gets into the far side of the furnace where the gas valve and electrical connections are. Any and all ideas, pointers or links to a walk through or manual on this would be greatly appreciated. Thanks, Lee

[showme]

Thanks very much for the information, guys. And sorry it took me so long to get back to reply. Once again I was waiting for an email to let me know I had replies. I'll let you know what I find. I should be going back down to the property tomorrow, so I'll go down these lists and see what I find. And thanks, Old Biscuit, for the link to the manual. I really appreciate the help, fellas. Lee

[enblethen]

Could locate the 12 volt wire and heat wire and jumper at thermostat,
I am thinking bad thermostat or no 12 volt power

[Old-Biscuit]

Suburban Service Manual....covers all models


SF wiring diagrams on pg 35
2000 vintage it probably is 2nd diagram with the 'Timed Delay Relay'
DC goes to one side of it and out other side to FAN Motor WHEN DC from T-stat goes to other connections on Relay

DC comes from a FUSED DC source...DC Dist Panel (15A Fuse)

Unfortunately....the SF Models w/o exterior access have to be removed from casing and bench tested

RV MFGs don't always account for repairs and make it difficult at best

Suspect TD Relay is bad.

[enblethen]

Verify 12 volts DC to furnace. Locate two blue wires in furnace. connect together to see if furnace runs. Separate wires to go into cooldown and shut off.