Furnace Fan Runs, but No Heat!

Discussion in 'Miscellaneous Repairs & Maintenance' started by rwright142, Sep 12, 2010.

  1. rwright142

    rwright142 New Member

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    This morning it was chilly so we wanted to test the furnace. I read the manual and followed it. I set the thermostat to 70 then clicked it on. After about 10 seconds the furnace fan came on but it only blew out cold air. Three minutes later still no heat so I followed the instructions in the manual and shut it off for 5 minutes and repeated the process 3 times but no luck. It does not have a pilot light but is equipped with an ignition device that automatically lights the burner. The only troubleshooting tip says if it fails to ignite 3 times to have it serviced. We have an electric space heater we will use until I can either troubleshoot this further or get it serviced.

    Anyone have some tips or experience to share?

    Thanks in advance,

    Richard Wright
    1995 Jayco 1206 KB
     
  2. Unstable_Tripod

    Unstable_Tripod Well, there's your problem!

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    Some furnaces have a Reset switch under the grille where the hot air comes out. Check to see if you have one and if so, if it's set to "On."

    Also, are you sure that you have propane in your tank and that the valve was open?
     
  3. rwright142

    rwright142 New Member

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    I have not read anything about a reset switch but I will check. I did not have any time to take the grill off but will do that next weekend. As for lp, yes it was good. I verified the refrigerator pilot was still lit. Also, I did not see anything about an lp switch for the furnace but I will check to see is there is one.

    Thanks for the reply!
     
  4. jjsul

    jjsul New Member

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    Richard,

    You didn't mention if you had used the stove first. I (and others here) have found that after a period of not using the propane system it will take awhile for the gas to reach the appliances. The usual easy fix is it light a burner on the stove as the stove burner provides an open source to "bleed" of the air in the system.

    Electronically fired Furnaces, hot water heaters, and gas refrigerators really require gas at the valve in order to light correctly. Pilot light based appliances will take a long time to bleed off air prior to lighting.

    Jerry
     
  5. rwright142

    rwright142 New Member

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    Hi Jerry,

    We did not use the stove this weekend but I had the refrigerator lit since Friday evening. We tried the furnace this morning (Sunday morning). Would that do the same thing? I have read where others say to use the stove first to get the air out of the lines and I don't know how the automatic burner works but I would think it would eventually light...

    Richard
     
  6. GCHIKER

    GCHIKER New Member

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    I MAY HAVE THE ANSWER

    Hey Richard, I had same problem with my new pup this past weekend. Then it hit me. The answer was in the actual description of HOW the furnace operates. It states that when the blower motor reaches 75% speed, the auto-ignitor sparks and starts the ball rolling. But alas, it wasn't doing that. After lots of head scratching, and coming to the realization that the blower motor kinda sounded a little slow, I plugged the pup into house current, flipped the converter switch to "converter", and SHAZZAM. Works great.
    Turns out the battery was low on charge or something was causing low voltage and the blower motor wasn't reaching it's required speed.

    Give that a try and let me know. (I hope my answer wins)
     
  7. rwright142

    rwright142 New Member

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    Dan,

    Thanks for the reply but I was already plugged in to the CG power. I'm searching for a manual to see if there is some kind of a cut off switch for the gas. We'll be camping this weekend but we will bring it home after that so I'll be able to work on it more then.

    Thanks for the reply!
     
  8. Gambit...

    Gambit... New Member

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    Here is a typical ignition sequence to help troubleshoot.

    Thermostat comes on, fan comes on, sail switch engages, delay to purge the burner chamber, ignitor and gas valve comes on, flame sensor tells the mother board the furnace is lit and to stop the ignitor and keep the gas valve on.
    Once the PUP is warm, the thermostat goes off, the gas valve is shut off, the pillum or burn chamber temp. swith keeps the fan on until the furnace is cool and then switches off the fan.
    There will be at least one if not several over-heat switches in this system and most bypass the motherboard and go between the power supply and the gas valve. If everything is working and checks out but, the gas valve still has no power, one of these switches either needs to be reset or replaced.

    Kim
     
  9. Davylee

    Davylee Camping = Life is Good

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    My atwood hyrdroflame II has a rocker switch under the grill of the heater if you see the red on top of the switch then the gas valve and ignitor should work. Also could be you got spiders/webs in there and the sail switch is not moving enough to start the ignition sequence. The on/off switch on the bottom of the thermostat is in the heat or on position correct?
     
  10. micbur

    micbur Working on "Camp Burton"...Opening Soon!

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    Question: Have you had your tank filled recently?

    I have had problems in the past with propane tank being over filled which has caused me problems. I had to bleed some of the propane out of the tank per the service department at the dealership where we purchased the PUP. They suggested disconnecting the hose from the regulator on the pup (after closing the valve on the tank) and then slowly open the valve. You should see the propane vapors coming out of the hose (make sure there are no open flames). Do this for 30-45 seconds then close the valve and reconnect the hose. Try lighting the stove first....if all burners are burning good then try the furnace.

    Not saying this is the problem but the two times I could not get the furnace to light I did this and it fixed the problem.

    I always light the stove first to make sure I have a good flow of propane...even though we never use the stove when camping.
     
  11. rwright142

    rwright142 New Member

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    I'll check the switch again this weekend. I saw that it was all black - did not see any red so I will look to see if it is not in the right position. I did verify that the on/off switch was on. This winter I will probably take the board out because it did look pretty bad. This camper sat in the Texas heat for years and mice did a number on it before the previous owner rebuilt it. He probably did not work on the furnace because he didn't need it so the board may be bad.

    No, we have not had the tanks filled recently.

    Thanks for all the replies!
     
  12. PattieAM

    PattieAM New Member

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    The typical sequence of the furnace is:

    Propane tank valve opened very slowly and lines purged of air.

    Furnace thermostat turned to 'on' position, and thermostat adjusted to temperature desired.

    Fan will come on and run for a minute or two and when running at proper speed (battery must deliver) the sail switch will open and you will hear ignition. (You will hear the ignitor click several times if there is not adequate propane). The furnace will run until temperature is achieved, then the burner quits and fan continues to run for a few more minutes.

    There is an "off/reset" switch behind the grill on my furnace, and I have to re-set it each time I disconnect the battery (when in storage).
     
  13. rwright142

    rwright142 New Member

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    Thanks for the reply. I have the camper at home now so I will look at it this week.
     
  14. riverwalker

    riverwalker New Member

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    Clean out the burner tube if you feel handy enough( not too hard)...or try cleaning out the intake an exhaust ports... use some high pressure air and a shop vac from the outside. if its been sitting any amount of time I'd bet the air flow is restricted and the burner tube if full of everything from bugs to mice droppings
     
  15. Atoyot1031

    Atoyot1031 New Member

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    9 times out of 10 when a part fails in the furnace system, it is the ignitor board. Universal replacements can be found for ~$100.
     
  16. rwright142

    rwright142 New Member

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    I bet that is the problem. It looks real bad.
     
  17. Atoyot1031

    Atoyot1031 New Member

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    It's fairly easy to troubleshoot to ensure that its not the ignitor, gas valve, etc. with a simple multimeter. If you have one and are inclined, let me know, and I'll put up some simple diagnostics.
     
  18. rwright142

    rwright142 New Member

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    Thanks for the offer. I don't have a multimeter but I can borrow one. Please reply with the diagnostics process.
     
  19. Atoyot1031

    Atoyot1031 New Member

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    How to troubleshoot a camper furnace ignitor board and associated components:

    1) Using your multimeter test before and after (with the stat in call) the thermostat for 12VDC. If you have power, procedd to step 2.

    2) With your multimeter, place the red (+) onto the gas valve lead, and the black (-) to ground. Put the thermostat in call. During the ingition sequence do you see 12VDC at the gas valve? If no, there is a problem with your board. If yes, proceed to step 3.

    3) Again put the furnace into call. After you see the 12VDC at the gas valve, smell the exhaust pipe for propane. If you do not smell propane, your gas valve is probably not working (assuming you checked your tank already). If yes, proceed to step 4.

    4) There are two wires comeing from your ignitor to your board. One is most likely fatter and orange and connects to a cylinder on your ignitor board. This is your ignitor/spark. The other goes to a 5 wire connector on the board and is your flame sensor (thermocoupler). Remove the ignition wire from the ignitor and carefully (not near the end) hold it ~1/4" from a solid ground. Place the stat into call. Do you get spark? If no, your board is dead, if yes proceed to step 5.

    5) Reconnect the ignitor wire. Place the stat into call again. Can you hear spark attempts (or see them through the sight glass)? If no, but yes on step 4, replace your ignitor. If no and no on step 4, it's still your board. If yes, proceed to step 6.

    6) Remove the ignitor. Visually inspect the ignitor for damage, corrosion, or breaks in the ceramic. If the ignitor is visibly damaged, replace. If not proceed to step 7.

    7) With the ignitor removed inspect the interior of the combustion chamber. Is the burn tube intact? Does it show any signs of corrosion or outside objects resting on it (dirt, rust flakes, debris, etc). If there is any debris remove with a vacuum. If the ignitor tube is corroded, replace.

    There are some other diagnostics steps you can take if you have ignition but it fails. However, these primarily address the flame sensor (thermocoupler) and the high limit switch.

    I hope this helps.

    Nick
     

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