Electric forced air heater will not turn off

Discussion in 'HVAC' started by seattlegooner, Jan 28, 2008.

  1. Jan 28, 2008 #1

    seattlegooner

    seattlegooner

    seattlegooner

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    I just bought a condo and before the deal went through, i had the seller replace all the electric forced air units as they were old. One of the three does not seem to register any type of temperature controls from the thermostat (a simple king single pole dial).

    I replaced this yesterday (being sure to hook it up exactly the same as before) but the problem still exists. When turned all the way down, it is off, when turned up, the heater comes on but will not shut off regardless of the temp in the room.

    My question is this... given that this was just replaced, if the person that did it accidentally swapped the wires, could this cause this type of behavior? i am hoping i can quickly fix this if so but don't want to go in and start swapping wires for the heck of it.

    thanks
     
  2. Jan 28, 2008 #2

    glennjanie

    glennjanie

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    Welcome SeattleGooner:
    I see no reason to believe the wires are hooked up backward. The thermostat simply breaks the power wires when the temperature is reached; sometimes this is accomplished by a small relay and sometimes by a contactor.
    Look in the heater's access panel and see if you can see a contactor which will have at least 2 wires hooked to each side of it. When the solenoid pushes the 2 metal contacts in they complete the circut and cause the heater to run. If it is a small brown box with a wiring diagram printed on it, that is a relay. Either way, if it has failed the supplier owes you a new heater; it shouldn't go out that quick.
    Glenn
     
  3. Jan 28, 2008 #3

    seattlegooner

    seattlegooner

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    thanks for the quick reply...

    so are you suggesting that the thermostat is trying to break the power but the heater is not registering this request?

    i am a novice at all of this (if you couldn't tell)....

    and how would i tell if the relay has failed?
     
  4. Jan 29, 2008 #4

    kok328

    kok328

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    Are the burners limiting in and out during cycles or is it the fan just won't stop running?

    Check that the fan switch on the Tstat is in "AUTO".

    Check to see if the Tstat is wired properly.
    Assuming a single stage unit (heat & A/C), they should be as follows:
    Terminal R = red wire = 24V
    Terminal C = black wire = common (if applicable)
    Terminal Y = yellow wire = A/C
    Terminal W = white wire = Heat
    Terminal G = green wire = Fan

    Check to see if you have a short in the Tstat wires. This requires a continuity test on the wires. Keep track of the combinations as you go, this can be tedious.

    I suspect that the white or green wire is shorted to the red wire. Tstat wire is typically solid core and doesn't hold up well to handling (i.e.- Furnance and/or Tstat replacment).

    If you believe the Tstat isn't even getting power, then you'll need to check the transformer. Should be 120VAC on the primary side and 24VAC on the secondary side.

    If all this fails you then you may have a bad time delay or a bad circuit board.
     
  5. Jan 29, 2008 #5

    inspectorD

    inspectorD

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    Wow what an explanation....nice.
    One other thing I have come across, bad wiring when it got pulled through a hole.
    Just a thought.:)
     
  6. Jan 29, 2008 #6

    seattlegooner

    seattlegooner

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    thanks for the detailed reply....

    also the burner stays on the whole time.
     
  7. Jan 31, 2008 #7

    kok328

    kok328

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    Sounds like a circuit board, bad tstat or limit switch issue. Even if your red and white wires were shorted, sooner or later the heat from the burners will limit out and shut down the burners until the limit switch resets and fires the burners back up.
    Are you seeing 24VAC on the white wire?
    What happens if you disconnect the red wire (at the board in the furnace)?
     
  8. Feb 6, 2008 #8

    kok328

    kok328

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    Just curious if we nailed this one or what ...
     
  9. Feb 8, 2008 #9

    triple D

    triple D

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    First of all, I believe we're talking about King wall heaters, not a central heat system. Second of all, I think I heard that when the thermostat is in the off position, the heater turns off, when the thermostat is rotated toward the comfort zone the heater turns on? This would mean that the thermostat, a simple two-wire device, is making and breaking a circuit by manual rotation, but failing to recognize the temperature of the room. Because you are experiencing this set of circumstances, this tells me you have purchased a bad thermostat and need to exchange it. Good Luck!!
     

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