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Author Topic: furnace blows cold air only, no heat  (Read 12664 times)

serrano31096

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furnace blows cold air only, no heat
« on: March 05, 2010, 09:18:33 PM »
Blows cold air only. It is a Suburban SF-30 about 15 years old. Thermostat works fine, sail switch is getting current. When I turn on the thermostat, it takes time for the blower to come on, then thats it. I don't hear any click click likes it trying to light. I turn the thermostat on and off several times. All the other appliances work great. Time delay has current, can't get to the high limit switch.  I could take it to the rv place, but they are expensive. Any help please.

Jim Dick

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Re: furnace blows cold air only, no heat
« Reply #1 on: March 05, 2010, 10:17:23 PM »
Sounds like the sail switch might be stuck or the gas valve is not operating. If you don't hear a fairly solid clunk a short time after the blower comes on then the valve is not opening. Might be the control board or the valve itself. Most of the time it's the board.

The board can be tested at an RV repair facility. Not sure if they would charge or not.
Jim

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Bob Buchanan

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Re: furnace blows cold air only, no heat
« Reply #2 on: March 06, 2010, 02:19:19 AM »
Thermostat works fine, sail switch is getting current.

That happened to me on a '94 MH. The repair guy found that tho the switch was getting current, the sail (he called it a paddle switch) was loose. When the fan motor started, the paddle would turn sideways letting the air pass without closing the circuit.
Bob (fulltimer - Rocklin, CA residency)
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DAN L

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Re: furnace blows cold air only, no heat
« Reply #3 on: March 06, 2010, 02:32:53 AM »
Blows cold air only. It is a Suburban SF-30 about 15 years old. Thermostat works fine, sail switch is getting current. When I turn on the thermostat, it takes time for the blower to come on, then thats it. I don't hear any click click likes it trying to light. I turn the thermostat on and off several times. All the other appliances work great. Time delay has current, can't get to the high limit switch.  I could take it to the rv place, but they are expensive. Any help please.

check these resources: i have the sf42 and replaced the wall  thermostat, about $100. that worked for a while, then nothing again. i replaced the circuit board (about $100) and all is still ok. that was about 2 years ago. good luck. :)

www.marksrv.com/furnace_trouble_shooting.htm
www.marksrv.com/suburbanparts.htm
http://rvbasics.com/techtips/rv-furnace-problems.html
01 Winnebago 35U W20. member Good Sam, SKP. all fluids AMSOIL Syn. BANKS ecm prog. SCAN G. II w/Alli temp. 4 KONI fsd shocks. 2 LIFELINE gpl-6ct Batts on their sides. TST t.p. and temp mon. K&N panel air filter. PROG IND inline surge prot. silv star lights. STEHL dolly. dw CHERYL, 2 cat furkids.

geodrake

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Re: furnace blows cold air only, no heat
« Reply #4 on: March 06, 2010, 06:29:29 AM »
Good luck.  I had the same problem.  Took it to CampingWorld.  They checked it out, found nothing wrong, charged me $70, and it has worked fine ever after. 

GO FIGURE!  I'm guessing there was a leaf, insect, etc. blocking the pilot and by driving to CampingWorld it fell off???????
George Drake

Clay L

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Re: furnace blows cold air only, no heat
« Reply #5 on: March 06, 2010, 08:33:40 AM »
Besides the sail switch and control board, another fairly common cause of failure is the high limit disk switch. If it opens and doesn't re-close it will cause the problem.
Clay (WA5NMR), Lee (Wife), Katie & Kelli (cats)
Settled down after full timing for eleven years and snowbirding for one year in a 2004 Winnebago 35N Sightseer, Workhorse W 20 Chassis. Honda toad

serrano31096

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Re: furnace blows cold air only, no heat
« Reply #6 on: March 06, 2010, 08:52:04 AM »
I put a volt meter on the sail switch. One at black wire hot and one at ground. This has current. Then I put one at red wire and one at ground and nothing, with fan running. Sail switch arm was up. I then put one at black wire and one at red wire and there was current. So, is the sail switch bad or good. Im confused now.

Punomatic

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Re: furnace blows cold air only, no heat
« Reply #7 on: March 06, 2010, 10:16:03 AM »
The first time I had this problem (NT 42T) I opened the combustion chamber and found about a cup of bees and other flying things. I cleaned them out and the furnace fired right off. The next time I had the problem, it was the high limit switch. The part was $12.45, and I was able to replace it myself.

Here is a link to a service manual for your furnace http://bryantrv.com/docs2/docs/SFseriesservice.pdf.
Here is a link to a troubleshooting guide http://www.gmceast.com/technical/Nicholls_Suburban_Furnace.pdf

If you are not familiar with working with gas appliances, it is best to take it to a qualified professional.
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Gary RV Roamer

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Re: furnace blows cold air only, no heat
« Reply #8 on: March 06, 2010, 11:27:46 AM »
We have our own Furnace Troubleshooting Guide in the forum Library.

I think its excellent, but I'm a bit prejudiced.  ;)
Gary
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serrano31096

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Re: furnace blows cold air only, no heat
« Reply #9 on: June 29, 2010, 03:51:24 PM »
Thanks for all the help. I found a manual online for my heater and went and check everything with a volt meter.
It turns out it was the circuit board. I ordered a new circuit board online for $120, not cheap but better then freezing.
Will we went camping last week and wow, we have heat. Thanks again. I love this site. :D