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Old 02-09-2009, 10:54 PM   #1
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1991 34' Limited
Port Orchard , Washington
Join Date: May 2007
Posts: 126
Suburban NT35K fURNACE update as requested by Peter Forwood

After a lot of research, I find that the Suburban furnace in my 34' 1991 AS ,a model NT35K, is just a larger version of the one in my old 1980 Winny MH, a model NT25K.
The main difference is the NT25K has one intake and one exhaust ports while the NT35K has one intake and TWO exhaust ports. Just more BTU's and more heat.
So repairs are not that much of a problem as I rebuilt the ol' Winny one.
Suburban does NOT offer a direct replacement for this furnace so a repair is the only way to go UNLESS you are willing to remove a section of
outside skin and CUT NEW hole for the intake & exhaust ports.
As I am not wanting to do that, I opted for a rebuild.

This furnace does NOT have any screws that connect the OUTSIDE ports to the furnace. There are only 2 screws that hold everything in place.
They are both inside the front cover and screw into the floor. However, this furnace DOES have a long over-lap of the exhaust / intake port tubes with the exterior port frames.
Remove those 2 screws, disconnect the wiring, the hot air heater ducts (4) and the propane line and out she comes.

The "sail switch" was not working 100% of the time. That was the problem with this 19 year old furnace. And I do not think the "module board" was too damn good either.

Both the ECO ("Energy Cut Off" or high temp cut out) & timed delay switch are working fine and check out well within specs.

After a complete dis-assembly and cleaning, I did not get as much dirt or rust as I expected.
The first photo shows, in the left half, the rust & dirt I collected form INSIDE & OUTSIDE the furnace. The right half shows the dirt from inside BOTH fan blades. Remember this is a 1991 model that had a VERY HEAVY SMOKING P.O. & she lived in this unit for over 5 years. Both batches of gunk are less than 1/16th" deep on the paper.

NOW, the 2nd photo shows the "module board" and why I do not think it works either... A picture is worth a 1000 smokes........

I am ordering all new, gaskets, a new Dinosaur Module Board, sail switch and maybe other parts tomorrow.

I have a question for "the lewster" about this furnace. I am wondering about the "Extend-A-Life" kit from Dinosaur Boards.
But I will discuss that in another topic. (THIS IS NOT NEEDED, IMHO and that of others.)


I have completed the repairs and have a few additions to make to explain the process for removing and replacing this furnace in this configuration where the furnace is located under the range & oven combo.

To successfully remove the furnace the first thing to do is TURN OFF THE PROPANE & ELECTRICITY ! ! !
2. Remove the furnace cover. 2 screws.
3. Disconnect the electric wiring to the furnace.
4. Disconnect the gas line using the CORRECT size wrench's. One for the brass nut & one for holding the gas valve. DO NOT USE ADJUSTABLE WRENCHES. JMHO.
5.Remove the FOUR 4" air ducts & the ONE small air duct that goes down into the holding tank area. I used a pair of side-cutters, as used to cut wire, and I just cut off the 2 pop-rivets that held the small air duct to the furnace case. This let me drop the small air duct down out of the way.
During re-install, I used 2 screws to secure the small duct as they where easier than trying to get the pop-rivet gun in there.
6. Remove the 2 screws that are located in the bottom front corners of the furnace case.
7. Remove the door to the "Folding chair storage compartment".
8. Remove the floor of the chair storage compartment. The floor in mine was held in place by 3 "pop rivets" along the outer wall bottom edge and 3 screws at the bottom edge of the panel that is used to cover up the back of the range & oven. The floor needs to be removed for when you try to re-install the furnace. My floor to the chair storage area was so tight down against the furnace that it would not budge and by removing the floor, the furnace slides right out.
9. Slide the furnace out from under the stove & oven.
10. Have a cuppa.. take 5.


12. After rebuilding the furnace, the re-installation is done in the reverse order UNTIL you try to get the one Intake port and the 2 Exhaust ports to line up with the exterior port pipes.. NOW you will see why taking the floor out of the chair storage area was such a good idea. With the help from a trouble light and my long arms, I was able to get the ports to line up. My knuckles where a little the worse for wear but that is not anything new. (I hate gloves so my knuckles get it all the time) After sliding the furnace back into place, continue with the re-install in the reverse order as you took it out.


While I had my furnace out and completely disassembled, I sanded the inside & outside of the outer case and painted the case with 1200 degree high temp paint. DO NOT GET ANY PAINT ON THE HOT AIR PLENUM AS IT WILL BURN OFF AND STINK FOR A VERY LONG TIME..........

My main repairs where to replace the SAIL SWITCH & the Module Board. I bought a Dinosaur Control Board (#UIB-S). The only brand to buy.
I ordered my parts from "Mark's RV Supplies in Albion, NY. Very good service.
I also checked the specs on the gas valve, Energy cut off switch, time delay switch and the fan motor. All mine were well with in the specs and should give me many years more service.

I bought 2 gaskets and made the rest by cutting them from the same white gasket material that is used to make EXHAUST HEADER gaskets for race car motors. I used a sharp EXACTO knife to cut them out. There is no metal in this type gasket material. You can buy this type gasket material at any good auto parts store.

AGAIN, BE CAREFUL and all will turn out OK.
stay warm.
One bazillion fish
1991 34' 60th Aniversary Limited Edition #008
2007 Chevy 2500 HD Duramax/Allison
One big parade float & a 40' Wells Cargo 5th wheel trlr.

"Wake each morning & Smile at the GREAT DAY you about to experience"
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