Suburban furnace fan lubrication

[richard5933]

Finally got the LP system checked out for safety and leaks. Everything seems okay, so I gave the furnace a try.

It fires up nicely and puts out decent heat. Model number is NT-32CD.

Problem is that the squirrel fan is in dire need of lubrication. It is slow to start, makes a decent squeaking noise until it ramps up, and really is working too hard. It ran enough to test it, but I wouldn't feel comfortable running it without doing some maintenance on the blower motor.

Unfortunately, they snookered the thing into a wall cabinet so tightly that I'm lost trying to figure out how to get to the fan. It is at the back of the furnace box. No access doors. No outside panel. Nada. Zip? According to the exploded diagrams in the manual, it looks like the rear panel may come off. Without pulling the furnace out, that won't be much help.

The front panel does come off, but all that is accessible from the front is the front end of the heat exchange unit. The fan is behind the heat exchange and the openings are only about 1/2 inch wide.

Any suggestions other than uninstalling the furnace and pulling it out? I'm pretty sure that if I could get some oil on the motor bushings things will be okay.



Richard
1974 GMC P8M4108A-125 (Current bus)
1964 GM PD4106-2412 (totalled Sept 2017)
Located in beautiful Wisconsin
KD9GRB

[Utahclaimjumper]

 For a very short time.>>>Dan

[richard5933]

For a very short time.>>>Dan

I've had success with other electric motor rebuilds in the past... Is there something unique about the motors in the Suburban? If so, once I get access I can replace it.

Starting to think that the only way to oil, repair, or replace is going to be to pull the whole furnace.

Richard
1974 GMC P8M4108A-125 (Current bus)
1964 GM PD4106-2412 (totalled Sept 2017)
Located in beautiful Wisconsin
KD9GRB

[lostagain]

I just finished fixing my Suburban NT40. The control board was bad. Anyway, I had to pull the whole thing out. Then the furnace itself slides out of a sheet metal cabinet. Then you have access to all the components. On mine the fan was noisy. Turns out it had slipped off its drive shaft enough to be rubbing on the housing. Pushed it back in, and it is quiet and free running again. The motor has sealed bearings, I don't think you could lube them. But yea, you'll likely have to pull the whole thing out.

JC

[buswarrior]

Welcome to the limitations of the less than thoughtful design execution ...

"Look how I craftily installed the device, it fits and it works..."

"What do you mean it will need repair sometime?"

"It won't be me having to do it..."

It's only funny until you're living it, then it is just tears...

You have fresh CO monitors? RV junk, first the fan, then the heat exchanger, and you don't wake up to that failure...

happy coaching!
buswarrior

[oldmansax]

I have oiled the Suburban motors also with varying degrees of success. Some (most?) use oil impregnated sleeve bearings. the sleeve gives up oil for the life of the bearing. When the sleeve runs out of oil, the motor squeaks. I have taken the motor apart and soaked the sleeve in oil for a couple of weeks. That seems to work best. A replacement motor is better.

As far as access, I'm guessing you are going to have to disassemble a bunch of stuff to get to it. They don't build these buses with service in mind.

TOM

[richard5933]

I just finished fixing my Suburban NT40. The control board was bad. Anyway, I had to pull the whole thing out. Then the furnace itself slides out of a sheet metal cabinet. Then you have access to all the components. On mine the fan was noisy. Turns out it had slipped off its drive shaft enough to be rubbing on the housing. Pushed it back in, and it is quiet and free running again. The motor has sealed bearings, I don't think you could lube them. But yea, you'll likely have to pull the whole thing out.

JC

When you pulled it out, what was the situation with the intake/exhaust ports? Looks like I remove the screws from the outside of the vent covers, and then the unit should slide out. Is this correct?

Richard
1974 GMC P8M4108A-125 (Current bus)
1964 GM PD4106-2412 (totalled Sept 2017)
Located in beautiful Wisconsin
KD9GRB

[lostagain]

Mine was a custom install, by the original converter. The intake hose is flexible and held on by a hose clamp. The exhaust is rigid steel, and just slides into a slightly larger fixed pipe that goes out through the floor and out the bottom. You'll just have to take sh*t apart until you get the thing out. Have fun.

JC

[lvmci]

My NT40 was taken out and reoiled and greased, the mechanic said fan motor was bad wouldn't last, didn't squeak for a couple months, no replacement available, had hoped to get a replacement at quartzsite, but no soap! lvmi...

[TomC]

When I built my bus, it took me much longer than most (6 years) because I went to great lengths to make everything serviceable. I can basically take everything apart in my bus if needed.
Although I have an Atwood 35,000btu propane furnace with exterior door, this is similar to yours. My old Atwood would just run on if left on without propane. I left the furnace on with the propane off. So when the temp got to low, the furnace came on. The fan ran for 2 weeds straight (bus is plugged in). The fan motor did not like this and became very tight and squeaking (sound familiar?). I tossed around to just replacing the fan motor, but read that the furnace had been updated with a quieter blower. I bought a complete new furnace (about $550) and yes the new furnace was quieter. The best update is that the new furnace has a blower overrun control that if the furnace doesn't detect heat (when the flame goes out), the blower runs for 2 minutes then turns off-even if propane is turned off.
My suggestion-just buy a new furnace. Good Luck, TomC

[richard5933]

...
My suggestion-just buy a new furnace. Good Luck, TomC

That was actually my first thought. Not sure if you can tell from the photo I posted, but there is ducting on both sides of the furnace as well as from the bottom. The new furnace which would replace this has a physically smaller cabinet. Sounds like this would make it easier to reconnect, but the configuration and layout makes it necessary to install elbows or adapters and there probably won't be enough room.

The other thing that is different on on the newer ones is that they seem to be either 12v or 120v. I initially thought that I had a 120v only unit, but apparently it can run off either 12v or 120v. I like that and would like to keep the option.

My first choice at this time is to get the motor serviced, repaired, or replaced if possible. The rest of the unit looks nearly new, so I have not found a reason (yet) to abandon it.

[lvmci]

Does the exterior holes for the vent match up?

[chessie4905]

If tht is original to the coach, I'd bite the bullet and buy a new one. Fit is the same, some higher output is available, see if you can make some accessibility while you are at it. Oiling motor will last shorter since it has to be removed or access and combustion chamber is how close to end of life. Clean it up, oil motor, sell it on Craigslist. One less thing on your repair/ replace list. After my father had the 4104 for 15 years, ( mid 80's conversion)while living in it from November to May, ( snow birds ), he replaced refrigerator, propane furnace, and icemaker. He also carried a spare shureflo water pump. He did oil the furnace fan motor every year on it. He was always very intensive on preventive maintenance on whole coach and conversion equipment.

[richard5933]

If tht is original to the coach, I'd bite the bullet and buy a new one. Fit is the same..

Fit is sort of the same, but not quite. I'm really hesitant to spend $500 or more on a new furnace, only to have to spend countless hours trying to figure out how to make it fit. Sure would seem easier to just repair, restore, or replace the blower motor. I do understand the point of not fully trusting a 43-year-old furnace though. In the end, some of this will depend on whether or not suitable install parts are available to fit something new into the same opening and use the same outside intake/exhaust holes.

The way the cabinetry was done in the Custom Coach builds makes it very difficult to modify things. They used custom cabinets which are screwed & glued together. The cabinets are made from 1-2 layers of 3/4" plywood and the whole thing is wrapped with Formica laminate. The corners are all rounded and the Formica bends around the radius. Once they got through with the build, the entire cabinet structure from one end of the kitchen to the other end by the wardrobe became a huge monolith. The furnace on ours is about 2/3 of the way down that wall under one of the wardrobe closets. Hopefully they left enough room to pull it out the intake opening. I'm not sure there is enough room to pull it straight out, and I'll either have to hope the bathroom door across the hall lines up enough or that I can turn it as it leaves the opening. The hall in front of the opening is barely as wide as the furnace is long. They certainly never thought that anyone would ever need to pull this out for service.

The duct on the right side of the furnace goes through the bottom of the wardrobe next to it. The walls and floor of the wardrobe are screwed & glued together. There is no way to access the other end of the duct to pull it off the furnace. I'll have to work in the 2" between the furnace and the right side of the space.

I guess convenience of servicing things was sacrificed to the desire to build a coach with zero rattles. That they did - this thing goes down the road with barely a whisper from the cabinetry and built-ins.

Okay - I'm done venting now.

I'll look at this again tomorrow when the sun is shining and the skies aren't so gloomy. Maybe I'll have a better go at it then.

Thanks for the suggestions.

[chessie4905]

Look up Suburban RV furnaces. They still have that model in identical dimensions and port locations.