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Thermostat no power/ fuses blown

I had no power to my thermostat.... there was a LED light blinking an error code that said secondary fuse open.... ichecked inside the panel area and there was a blown fuse on
the circuit board, after i replace the fuse...the LED light was on continuously which said the system was getting 24v...I set the thermostat to fan and it kicked fan on, i set it to auto and set the heat up but it would not kick on.. then i went back down and both the internal circuit board fuse and external circuit board fuse were blown???

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  • woockman1 May 09, 2010

    sorry i am somewhat of a novice... i have a multimeter but how do i check the continuity of the thermostat wires? my black prong(multitmeter) on common wire? red prong(from multimeter) on each of the others individually? with the AC setting? or ohms? 0.00 for good any reading for bad?

  • woockman1 May 09, 2010

    I went down the furnace unit and jumped the green and red wire... then i went up to the thermostat and the ohms were 0.06 from green to red....also did this with common and green same thing...so i assume that means we have continuity for these wires..Does that mean no shorts in those wires?



  • woockman1 May 09, 2010

    Also i shut off the thermostat and did ohms from green to red i got a reading and also got a reading from common to green...so no continuity while system off

  • woockman1 May 09, 2010

    very possible....



    When i replace the fuses the fan alone will work and power is back to stat...as soon as i switch it too "auto heat" i hear it try to kick on and then it blows the fuse, does this make sense with a bad board?

  • woockman1 May 09, 2010

    How do i test the element?/ where exactly is this. i have a multimeter...but explaining exactly where to test it would be appreciated



    my furnace is a payne model # pg9maa036080

  • woockman1 May 09, 2010



    http://www.docs.hvacpartners.com/idc/gro...



    It is very similar to this...if not the same but older model...




  • woockman1 May 11, 2010

    Just wanted to thank the first solution guy he had it right a shorted wire i just didn't look close enough outside in the condensing unit. found the short...back in business

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This has happened because of an Overload, probably a short circuited element, you need to test the element. you should not just ever replace fuses without first finding out why. it happened. Any circuit, of any heater is pretty basic, usually, we have a switch, a thermostat, a thermal fuse, and an onboard fuse, terminating on the element, returning on the neutral. It works basically, by the switch puts power to unit, this powers the electronics, which monitors the thermostat,that has contacts in series in the Phase wire, before the element, when the thermostat's temperature is reached the Contacts, OPEN, and cut power OFF to the element, it cools down, and it turns ON again, over and over keeping the temperature constant. There is a Power fuse, in case of a short circuit, or overload, and generally an "Over heating" or "Thermal Fuse" too. All fuses are in the Phase Line, and break the circuit when activated.

Posted on May 09, 2010

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Replace the fuse after reading the fuse specification in thermostat manual....
If the fuse is heavy bonded, then it will not blow when there is a need.... It will make other components to blow....
So replace all the fuses only according to the specification...
fuses varies according to the thickness off the wire used in it...which is directly proportional to the resistance....
so use only recommended fuses with recommended value...

Posted on May 10, 2010

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You must have a shorted thermostat wire somewhere. Turn the thermostat off and check for continuty between the wires coming from the stat. You should have no continuity since that stat is off amigo. If you have continuity that would confirm bad thermostat wires.

Posted on May 09, 2010

  • 7 more comments 
  • Dan Webster
    Dan Webster May 09, 2010

    Here is multimeter directions.
    Basically set the meter on audible beep for continuity or the needle hops over whn the 2 leads are touched together thus proving a circuit right? Then remove the wires to the thermostat and check for a beep with the thermostat off. If you gt continuity then the wires are rubbing and shorting out the transformer.


  • Dan Webster
    Dan Webster May 09, 2010

    Let me know

  • Dan Webster
    Dan Webster May 09, 2010

    I would get a pro out there. You need a board change out most likely.

  • Dan Webster
    Dan Webster May 09, 2010

    Is your furnace similar to this one PAYNE FURNACE

  • Dan Webster
    Dan Webster May 09, 2010

    Check your transformer. It could be shorted out.

  • Dan Webster
    Dan Webster May 09, 2010

    Look on the board for something shorting it.

  • Dan Webster
    Dan Webster May 11, 2010

    Thanks. Glad you got her done amigo!!!

  • Dan Webster
    Dan Webster May 12, 2010

    Thanks!

  • Dan Webster
    Dan Webster May 12, 2010

    Thanks for the great rating and the rejection. Lovs dat.

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