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Topic: Furnace problem - maybe? (Read 954 times) previous topic - next topic

Furnace problem - maybe?

After I got the coach moved a bit so I could plug it in I turned on the furnaces on a low setting, with the idea that we might move into the coach should this blizzard actually amount to something. The front furnace has worked perfectly, but the rear one has me concerned. The blower would run constantly, but it didn't seem to be producing any heat. I've turned the furnace off, let it sit for at least five minutes, and then restarted it. Each time I do, it will work fine for a while, but eventually it doesn't produce heat anymore. The furnace is actually right outside my window as I type this, so I can hear it cycling on and off. I'm going to put a screwdriver right by the front door, and the next time the furnace cycles on I'll run out and see if I can see a flame somewhere.

Which furnace provides heat to the tanks, front, rear, or both? Do I have a problem here, or is this normal?

Re: Furnace problem - maybe?

Reply #1 –
On our '93 U300/36, only the rear furnace supplies heat to the belly. After the rear furnace has been switched on, you should be able to go outside and feel the hot exhaust. Hot enough so you can't keep your hand there.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Furnace problem - maybe?

Reply #2 –
I have felt it, but most of the time it is blowing cool air. Right now it seems to be working properly, so maybe it just needed to be run a bit. I'll see what it is doing later on, and if there is time I'll check it in the morning before I go to school (assuming that we do have school tomorrow).

Re: Furnace problem - maybe?

Reply #3 –
You probably know it but after the room has reached the thermostat temperature, the burner will shut off but the blower will still continue to run until the burner temp drops down so heat soak won't damage any components or catch anything on fire. So the exhaust temperature will be cool for a minute or two before the furnace shuts down completely.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Furnace problem - maybe?

Reply #4 –
I just went out to check on the furnaces. The blower was running, but no heat, and a nice little mound of snow on the exhaust. The temperature in the bedroom is about 55, and about 65 in the front. When I went outside just now the front furnace was running, but it stopped as I was unlocking the door. There was no air blowing from the front vents. The rear vents had cold air blowing out of them. The front furnace lit while I was out there, and hot air came from the vents. I'm guessing that when the rear burner shuts off it doesn't start up again and the blower keeps on blowing. I'll poke around at it Saturday.

While I was typing I heard the burner shut off, so I went back out in the snow. The front furnace was quiet, but the blower was going on the rear one. Within a minute it stopped. I stayed out, and pretty soon the blower came on in front, followed by the burner. Then the rear blower came on, followed by the burner. I guess as long as I'm out there the furnace will work! No, I'm not going to spend the night standing out in the snow watching the furnace.

Re: Furnace problem - maybe?

Reply #5 –
David,

Does the rear furnace have a dauber screen? We lost the burner in the rear furnace because daubers had clogged it. It looks like they partially clogged it and it overheated in other areas. Ours quit altogether. Wayne at FOT fixed ours. Yours might be partially clogged so that it doesn't properly sustain a flame.

It could also be a propane pressure issue or a dirty orifice.
J D Stevens
1997 U295 CAI 36' Build #5085
2002 Subaru Outback
Motorcade 16869
Bellville, TX

Re: Furnace problem - maybe?

Reply #6 –
David,
JD's point on the dauber screens is well taken!  Daubers love propane and will seek the furnace burner out, if not prevented by screens.  First change we made to our coach!
Also, you need to read Barry's thread regarding "Short Cycling" of the furnace. 
If the furnace's high plenum heat safety thermostat is short cycling the furnace (a common problem if outlets are "gagged down") your rear furnace would perhaps behave this way. 
It may well seem that the furnace is blowing more cold air than hot (burner is shut off longer than it is turned on),  and that may be just confusing you.  You need to check to see if all of the rear furnace heated air outlets, in the aft of the coach and in the basement, are as open as they can be (maximum air flow).
I would verify vents maximum open.  Then try increasing the wall thermostat target temperature by a large amount, say 20 to 30 degrees above ambient.  Then use a watch and chart the times of the burner on and off cycles. I'd also  chart the temperatures fore and aft in the coach.  If the furnaces are both firing,  temperatures are coming up and the the short cycling has a rather predictable pattern to it, then it may just be the short cycling issue, which Barry's thread gives more insight to.
Neal

Propane furnace cycling
The selected media item is not currently available.
Neal (& Brenda) Pillsbury
'02 U320 SPEC, 4200, DGFE, Build #5984
'04 Gold Wing
'07 Featherlite 24'
'14 Jeep Grand Cherokee Summit
MC #14494
Exeter, NH & LaBelle FL
Quality makes the Heart Soar long after Price is Forgotten

Re: Furnace problem - maybe?

Reply #7 –
I have always worried about losing one of the furnaces in really cold weather. I just hate the cold. Even mid-west humidity with triple digits in the summer is not as bad.

I installed an unvented heater in the main salon. It raises the humidity a bit and you have to remember to open the window or you might not wake up but in an emergency, it takes zero electricity and is almost 100 percent efficient.

You really need an accurate CO detector as CO, high altitude and heart conditions don't go together. Does no good to step outside if your blood CO level is high either.

Here are a couple of shots.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Furnace problem - maybe?

Reply #8 –
The furnace has worked FB for the past few days and nights, so maybe it was just in need of being used.

Re: Furnace problem - maybe?

Reply #9 –

Quote from: kb0zke –
The furnace has worked FB for the past few days and nights, so maybe it was just in need of being used.
FB ??
                
    • Fly ball
          
    • Fast busy
       
    • Fine business
                         [/list]Neal
     
    The selected media item is not currently available.
    Neal (& Brenda) Pillsbury
    '02 U320 SPEC, 4200, DGFE, Build #5984
    '04 Gold Wing
    '07 Featherlite 24'
    '14 Jeep Grand Cherokee Summit
    MC #14494
    Exeter, NH & LaBelle FL
    Quality makes the Heart Soar long after Price is Forgotten

    Re: Furnace problem - maybe?

    Reply #10 –
    FB= Full Bore??
    Nitehawk,  Demolition Lady, & our NEW master, Zippy the speeding BB cat.
    1989 Grand Villa 36' ORED
    Oshkosh chassis, 8.2 DD V8
    2006 Saturn Vue AWD

    Re: Furnace problem - maybe?

    Reply #11 –
    FB = "for better" (as opposed to "for worse")?  ::)
    The selected media item is not currently available.Pat Hatfield
    2000 U295 3600 #5666 WTFE (sold 1/7/20)
    2014 Jeep Grand Cherokee
    previously: 2003 U295 3610 #6228 (sold 5/29/14)
    previously:  2009 Honda CRV (sold 6/9/14)

    Re: Furnace problem - maybe?

    Reply #12 –
    Nitehawk,

    If FB = Full Bore (for past few days and nights), then standby for meltdown!

    (It needs to cycle or it's not working correctly).

    Neal
    The selected media item is not currently available.
    Neal (& Brenda) Pillsbury
    '02 U320 SPEC, 4200, DGFE, Build #5984
    '04 Gold Wing
    '07 Featherlite 24'
    '14 Jeep Grand Cherokee Summit
    MC #14494
    Exeter, NH & LaBelle FL
    Quality makes the Heart Soar long after Price is Forgotten

    Re: Furnace problem - maybe?

    Reply #13 –
    Sorry, I had the radio on when I was typing. FB = Fine Business = working properly.

    Re: Furnace problem - maybe?

    Reply #14 –
    Ha, there seems to be no end to the FB meanings.
    Using a iPad, too hard to list another dozen, but
    FB-Fat Back
    FB-Freaking Busy
    FB-Free Beer
    FB-Foul Breath
    FB-Fresh Biscuits
    No end----
    I enjoy word games, how many words can you make out of Thanksgiving ?
    etc
    Smile
     

    Re: Furnace problem - maybe?

    Reply #15 –
    Pierce
    Would you please pass along the name and model of your neat little heater. I think it will heat my 2900 without a problem.

    Edit,
    I like free beer and free biscuits. Sounds like a meal to me. :)
    Michael j
    Livermore, Ca for now

    1987  Grand Villa 2900 Rear Bath Front 460 Gas Engine.