HVAC blower turns on when system is off

Discussion in 'HVAC' started by Peterc, Jun 21, 2014.

  1. Jun 21, 2014 #1

    Peterc

    Peterc

    Peterc

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    My Goodman gas furnace/AC unit will turn on the blower fan when my thermostat is in the off position. I have attempted to reset by pulling the front panel of the thermostat off, raised the on temp for A/C far above the current room temp but fan continues to periodically turn on.
    Any thoughts?
    Thanks,
    Peterc
     
  2. Jun 21, 2014 #2

    Wuzzat?

    Wuzzat?

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    Intermittent short in the 'stat, wall wiring or furnace. If this happens often you have a good chance of tracing it down with a multimeter.
     
  3. Jun 21, 2014 #3

    carnuck

    carnuck

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    Actually, depending on code in your area it may be neccessary for ventillation if you have a super insulated house.
     
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  4. Jun 21, 2014 #4

    Wuzzat?

    Wuzzat?

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    Today I have learned something. :) Numero uno pregunta in troubleshooting: is it designed to do this?

    This particular feature should be listed in the 'stat manual so step number 0 in troubleshooting is: read all manuals.
     
  5. Jun 22, 2014 #5

    Peterc

    Peterc

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    Manuals read (about the 3rd time for various reasons) and find no reference to blower turning on automatically when system is off. The only similarity is the duration of time blower is on, about 2 minutes or the same as if the heat was initiated but the ignition did not take place.

    Question: what is the 'stat wire?

    Thanks, Peterc
     
  6. Jun 22, 2014 #6

    Wuzzat?

    Wuzzat?

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    Sounds now like the problem is in your furnace and you have two minutes to trace down the source of that false signal, until the next time.
    For this kind of problem I put appropriately wired LEDs on several test points and when the problem shows up the LEDs that are on or off tell pretty quickly where the problem is.
    That's a little beyond DIY stuff.


    'stat = t'stat = thermostat.
     
    Last edited: Jun 23, 2014
  7. Jul 10, 2014 #7

    Peterc

    Peterc

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    With limited time to catch the fan on problem, I finally heard the air blowing/sucking from the vent pipes outside the house. I later identified that this happens WITHOUT after I disconnected the thermostat from the wall. I still can not find anything that says this is a normal function. Guess I'll bite the bullet and bring in the A/C people.

    Thanks,PeterC
     
  8. Jul 10, 2014 #8

    Wuzzat?

    Wuzzat?

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    With your reproducible symptom the HVAC people should be able to give you estimates, the minimum expected, and the maximum expected, cost.

    If their minimum is $100 and their maximum is the same as the price of a new furnace, they have told you nothing of value. The range is too wide.

    It's not like they have no idea what's causing this.

    Call at least five places.

    Another option is to go to an HVAC parts place and ask what part for your furnace is sold the most often, and what is sold the least often.
    I did this with a Stihl leaf blower: they are not DIY-friendly and I suspected the magneto but the parts guy said they hardly ever sell any of those. BTW, it was a $3 jet that a repairman for a rental place clued me onto.
     
    Last edited: Jul 10, 2014
  9. Jul 11, 2014 #9

    CallMeVilla

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    This is a very helpful video which takes you thru a diagnostic step-by-step.

    [ame]http://www.youtube.com/watch?v=81-RGI8pCno[/ame]

    If you cannot solve it with this approach, you might have to get a tech out to fix it.
     
  10. Jul 11, 2014 #10

    Wuzzat?

    Wuzzat?

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    For outside HVAC work, I recommend
    a dry board to step on so you aren't grounded
    a flashlight, even in the daytime
    a tray on the ground so you won't lose the small parts you will drop in the grass
    insect repellent
     
  11. Jul 14, 2014 #11

    carnuck

    carnuck

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    A vacuum to remove spider webs helps too.
     
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  12. Sep 20, 2014 #12

    Peterc

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    Hi All,
    Eventually I found out the "venter blower" is what turns on which in turn points to a short or bad circuit board. I've purchased a new circuit board which contains a 9 pin connector. There is a new 9 pin connector with 5 empty slots for wires from the old connector. PROBLEM is I have not been able to remove wires from the old connector.
    QUESTION, can I simply plug in the old connector into the receptacle on the new circuit board. All the wires match but I hate to do this if there is some not too obvious problem doing this.

    Picture of original connector attached.

    Thanks,
    PeterC

    Orig 9 pin block.jpg
     
  13. Sep 20, 2014 #13

    CallMeVilla

    CallMeVilla

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    Nice to see he came back with what happened ... :banana:
     
  14. Sep 20, 2014 #14

    bud16415

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    If you can't get the connectors off easily I don't see anything wrong with using the old wires and connectors.


    Sent from my iPhone using Home Repair
     
  15. Sep 20, 2014 #15

    Peterc

    Peterc

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    Thanks,

    I'll plow ahead using the original 9 pin connector.

    PeterC
     
  16. Sep 22, 2014 #16

    Raindem

    Raindem

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    Funny, but my roof mounted AC/Heater combo unit started doing this last night. But it's more random. Every 2-3 minutes it turns on. Sometimes it runs for a minute, other times just a couple seconds.

    So Peter, how did you figure out that it was a circuit board? I have a multimeter but I don't really know where to start looking.

    Thanks

    Curt
     
  17. Sep 24, 2014 #17

    Peterc

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    1st let me thank everyone as there were bits and pieces of many of the replies that I used to eventually solve my issue. The bottom line is that I have replaced the circuit board and everything works fine. Yesterday I had the A/C on for some time with no problem. Tonight at 50 F the heat seems to be functioning as I would expect.

    Thanks to all.
     
  18. Sep 24, 2014 #18

    Peterc

    Peterc

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    Curt,
    My problem with the inducer motor turning on when the termostat did not call for heat was always random but became very frequent as time went on. This would happen when the thermostat was in the "off" or "cool" setting. I could not find any tie in with a multimeter except when venter began. I could not trace back to any thing. My testing began with pulling connections but the inducer motor would eventually turn on. After pulling all the connections to the blower motor and pulling the thermostat from the wall, it pointed back to a short and by the process of elimination an HVAC firm was more convinced that it was the circuit board. So for about $100 I decided to do the circuit board because the weather was turning and I had to do something soon.

    Any other questions let me know.

    PeterC
     
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