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Topic: Furnace Question (Read 964 times) previous topic - next topic

Furnace Question

I have the 8535 IV furnaces in my 1989 Unihome. The rear one works perfect. The front one however has a slight problem. When I set the NEW thermostat to the desired setting it begins operations fine. (Blower turns on, ignites, fires, blows warm air). Here is the problem. When the desired thermostat setting is reached the furnace begins to shut down properly, but while the blower continues to blow (cooling down the firebox) the ignitor fires again, blows hot air, shuts off, blows to cool down, fires again, blows, shuts off, blows to cool down. It continues to do this until I set the thermostat to the off position. My question(s) is has anyone had this problem and what was the solution? I am a full-timer and am really going to need this fixed come December. :) Thanks for any help in this matter.

Courteously,

Curtis
Curtis
1989 GV

Re: Furnace Question

Reply #1 –
I'm thinking you wired the digital thermostat wrong.  Which did you get, a Hunter?
1994 U225
build #4514

Re: Furnace Question

Reply #2 –
First, it is not a digital thermostat, but it is new. It has two wires; similar to a electric on and off switch only the "lever" is a bi-metal sensitive to the temperature. It would be nearly impossible to wire it up wrong, I believe. It is a simple analog Suburban brand. The original Hydroflame gave the same symptoms along with one other analog bi-metal residential "round" thermostat. Thanks though.

Curtis
Curtis
1989 GV

Re: Furnace Question

Reply #3 –
Curtis,

First thing I would do is to pull the connection off the PC board (outside furnace door) and clean with a good electric cleaner and reattach. 

Would be interesting to see if the thermostat is calling for the cycling or if it is the PC board. Have you used an ohm meter on the two wires from the thermostat to see if the cycling is coincident with thermostat on/off? Some thermostats have an adjustment for range between off and on.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Furnace Question

Reply #4 –
Mr. Wolfe,

I cleaned all the contacts originally because it would not run. I pulled each connection off, sprayed both with industrial contact cleaner, and then reattached. Now it runs but with this problem. I will check with my ohm meter this weekend. Thanks.

Curtis
Curtis
1989 GV

Re: Furnace Question

Reply #5 –
Mr. Wolfe,

The original thermostat was set at 0.4 vs the new one at 1.2. I set the new one now to 0.4 and seems better, but I will watch it for a week. On a side issue. The changing of the outside light to a clear lens and 12" water-proof led strips. NNIIICCCE. I used four strips though. :) Thanks again for all the great help. I would be lost without you folks.

Curtis
Curtis
1989 GV

Re: Furnace Question

Reply #6 –
It appears that you have the same furnace in both the front and back of the coach. If so, you can take the control board out of the one that is functioning properly and install it in the other one. If it acts the same with th other board in it, the problem is probably with the thermostat. If it starts working properly try the bad board in the other furnace to confirm that the board is bad. Once that is confirmed, purchase a new board and you should be good to go.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: Furnace Question

Reply #7 –
I had a similar problem one furnaces PC board was bad not shutting down the furnace blower I would follow Kent's suggestion swap the board both furnaces are the same.

I believe the new board cost about ~$125 not including labor. The work was done at Keystone RV in PA, I did receive motorcade discount, do not have receipt handy, but I believe my  total cost with labor was about ~$210.

Tony
Tony Pasquale
SOLD....
'99 U295 36'
WTFE, 04/99, #5572
Toad: 2020 Equinox

Re: Furnace Question

Reply #8 –
It would be easier to try the known good THERMOSTAT from the bedroom first, then troubleshoot the furnace if the problem persists.
1994 U280, Build 4490
Deming, NM.

Re: Furnace Question

Reply #10 –
Quote from: David Smith –
If it is your board go to Dinosaur Electronics Home. High quality circuit boards for RV appliances..  Good quality products at good prices for RV.

And a great warranty on their boards. I had a fairly new board fail, <2yrs old, called and gave them the serial number, they sent me a new board with no hassle.
Roland
1993 U280 4341
2010 Jeep Liberty
The Pied Pipers

Re: Furnace Question

Reply #11 –
Thanks everyone. I didn't even think to use the rear one's parts to "shoot" the front one. Like my father told me, "No one is as smart as all of us." I looked at the old thermostat and then the one in the rear, they were both set at 0.4. The new one was set at 1.2. I set the new one at .4 and the front furnace works perfect. Thank you all again, your are all such a wealth of knowledge. Blessing to all.

Curtis
Curtis
1989 GV

Re: Furnace Question

Reply #12 –
Also, I am located in Marion, Indiana. There is a surplus RV store called Ickes RV about 25 minutes east of Marion on St. Rt. 18. This place is great, and so are the prices. Thanks.
Curtis
1989 GV