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NEED HELP with Garage furnace!

Discussion in 'Off Topic Threads' started by Tron, Sep 21, 2012.

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  1. Tron

    Tron Supporting Vendor Supporting Vendor

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    I have a 60,000 btu Modine Hot Dawg natural gas furnace (11 years old) that refused to turn on for the first cold morning of the year. All I get is a low humming noise from a part that has a tube running to the exhaust fan. The gas valve has a green light that continously flashes. Can anyone help me out with diagnostics?

    Part that hums:

    <a href="http://smg.photobucket.com/albums/v712/Tronspace/?action=view&current=DSCN1134_zpsd170861b.jpg" target="_blank"> DSCN1134_zpsd170861b.jpg </a>
    <a href="http://smg.photobucket.com/albums/v712/Tronspace/?action=view&current=DSCN1133_zps1653d471.jpg" target="_blank"> DSCN1133_zps1653d471.jpg </a>

    Jb
     
  2. Auctioneer

    Auctioneer Well-Known Member

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    If you have a 11 year old furnace your done well with it. It might be time to replace it. We had to with one of ours. It was 12 years old.

    It could be the board that lights up the furnace. It might have a crack on it like we had one time. Once replaced it wrked fine.
     
  3. Joen

    Joen Member

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    That looks like a pressure differantal swicth that proves that the exhaust fan is running check the exhaust for a
    1. if you you have the owners manaul it will tell you what the different lights flashings mean
    2. check for bird nest or anything blocking the air flow of the exhaust
    3. take the tube off of the swicth to make sure it is clean
    4. try using a jumper wire to jump the switch to see if it will run if so either the switch is bad or there is a air flow restriction or exhaust fan is bad
     
  4. Stl Flyn

    Stl Flyn Well-Known Member

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    The fan should start up when it is first calling for heat. Seems the fan would be the problem as mentioned above.

    The switch mentioned, controls when the burner ignites. When the thermostat is first calling for heat, the exhaust fan, or power vent should go on to clear the flu of any excess gas. The orange tube then creates pressure on the switch diaphragm, caused from the air blowing in the end of the tube in the vent. This in turn creates the contacts in the switch to connect, telling the main gas regulator it is clear for ignition.

    I had this go out on my hot water heater. I took the tube off from the vent and created some pressure on the tube. The burner then ignited. If you do this make sure there is no excess gas in the burner area. My fan was working so it cleared the excess gas. The pressure switch was defective so the power vent was working when it ignited.
     
  5. X Trap 2

    X Trap 2 TS Member

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    Make sure kitty did not make a nest up there. Ray
     
  6. Tron

    Tron Supporting Vendor Supporting Vendor

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    Ok, update. I was wrong about where the humming noise is coming from. It's actually coming from what appears to be a transformer or relay (on far right of pic) and the noise was telegraphing through the metal to that diaphram because it has better accoustics.

    <a href="http://smg.photobucket.com/albums/v712/Tronspace/?action=view&current=DSCN1136_zpsbce96de1.jpg" target="_blank"> DSCN1136_zpsbce96de1.jpg </a>
     
  7. Auctioneer

    Auctioneer Well-Known Member

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    Did you check the board that lights the furnace? My furnace doesn't have a pilot light that stays on all the time. It only comes on when the furnace lights up.
     
  8. ScottEslick

    ScottEslick Member

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    Joe,

    Show a pic of the burner assembly, if it has an igniter that could be the problem, most of them are line voltage and are easy to check.

    Scott
     
  9. Catpower

    Catpower Molon Labe TS Supporters

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    That's the control transformer that is humming

    Does the inducer fan motor start? That's the little motor by the diaphragm switch

    The sequence of operation in when the T'stat calls the inducer fan motor starts and purges the exchanger of any possible gas, when it starts the diaphragm switch makes to prove the fan is blowing after a few seconds you will either start heating up the hot surface ignitor or it will start sparking depending on what type of ignition it uses, hot surface will start to glow, spark will spark, after a few seconds the gas valve will open the burners will light then the main fan will start.

    As said in the owners manual of on one of the stickers on the unit there will be a code for the flashing LED, but flashing green might mean it's working, generally a fault is a yellow or red LED
     
  10. Tron

    Tron Supporting Vendor Supporting Vendor

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    Well, for whatever reason, it started working again. That's weird.
     
  11. Catpower

    Catpower Molon Labe TS Supporters

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    Sometimes they will lock out on the first trial for ignition, it's really not that rare

    There is a possibility that the flame sensor is dirty, it's the little rod that sticks down in the flame at the opposite end of the gas manifold, if they get rusty it won't conduct electricity to prove the flame through rectification, if it happens very often you might need to take the flame sensor out and use some fine (500 or so) sand paper and shine it up
     
  12. grntitan

    grntitan Well-Known Member

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    Heck, the best kind to have. Self fixing. You have all the luck Tron. Me, I just replaced my hot water heater last week and my AC went out the day before yesterday. I'm tapped out to say the least.
     
  13. Ducky

    Ducky Member

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    My garage heater got a crud ball in the hose form the fan housing to the diaphragm sw. That kept the sw from tripping and turning on the burner. Cleared it out and was AOK after that.
     
  14. Harv Shell

    Harv Shell TS Supporters TS Supporters

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    Joe, use a green scotchbrite pad to clean the sensor. Any sandpaper will put tiny scratches that will make the sensor foul even quicker. Harv
     
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