Carrier furnace fan won't switch on

Discussion in 'HVAC' started by Augment, Apr 7, 2010.

  1. Apr 7, 2010 #1

    Augment

    Augment

    Augment

    Member

    Joined:
    Apr 7, 2010
    Messages:
    22
    Likes Received:
    0
    I have a 10 year old Carrier furnace. When in heat/ac mode the fan will work, but it won't run continuously in "on" mode. When the heat/ac is "off", and the fan is "on", it won't work at all. It used to work continuously when in "on" mode. The blower motor was replaced a few months ago and the problems started then. The LED light is not showing any problems. Is there a quick fix?
     
  2. Apr 7, 2010 #2

    kok328

    kok328

    kok328

    Well-Known Member

    Joined:
    Nov 20, 2007
    Messages:
    2,755
    Likes Received:
    249
    Check to see if the green wire or wire from the G terminal on the thermostat is hooked up and likewise at the thermostat terminal connections inside the furnace.
     
  3. Apr 7, 2010 #3

    Augment

    Augment

    Augment

    Member

    Joined:
    Apr 7, 2010
    Messages:
    22
    Likes Received:
    0
    yes, the green wire is hooked up on the thermostat and the furnace.
     
  4. Apr 7, 2010 #4

    kok328

    kok328

    kok328

    Well-Known Member

    Joined:
    Nov 20, 2007
    Messages:
    2,755
    Likes Received:
    249
    What happens when you jumper 24V from the red wired to the green wire?
    If you remove the furnace panel door, make sure the safety switch doesn't cut power to the unit while testing.
     
  5. Apr 7, 2010 #5

    Augment

    Augment

    Augment

    Member

    Joined:
    Apr 7, 2010
    Messages:
    22
    Likes Received:
    0
    I wouldn't know how to do that - please explain!
     
  6. Apr 7, 2010 #6

    kok328

    kok328

    kok328

    Well-Known Member

    Joined:
    Nov 20, 2007
    Messages:
    2,755
    Likes Received:
    249
    Oh sorry, sometimes I assume too much.
    Take a piece of wire and strip the two ends.
    Touch one end to the "R" terminal and the other end to the "G" terminal on the thermostat terminal strip inside the furnace.
    As I mentioned, there may be a safety switch that will kill power to the unit when the access panel is removed. For the most part, you can just hold this in to restore power while testing.
    Jumpering the R&G should run the blower motor.
     
  7. Apr 8, 2010 #7

    Augment

    Augment

    Augment

    Member

    Joined:
    Apr 7, 2010
    Messages:
    22
    Likes Received:
    0
    What would I be achieving by doing this? I'm reluctant to try anything without knowing why I'm doing it. The blower motor does work if it's in heat mode, just doesn't stay on continously even tho the fan setting on the thermostat is set to "on".
     
  8. Apr 8, 2010 #8

    kok328

    kok328

    kok328

    Well-Known Member

    Joined:
    Nov 20, 2007
    Messages:
    2,755
    Likes Received:
    249
    I'm trying to guide you in troubleshooting the circuitry of the unit. This will basically tell us if the T-stat is bad or if there are other issues preventing the fan from working in the "On" setting. It's only 24VAC so no safety issues to be concerned about. If you prefer an alternate technique, you'll need a voltmeter. Turn your tstat to fan "On" and check for 24VAC from ground to "G" (green). This will tell me if the tstat is energizing the fan circuit or we can just energize it and see if the fan comes on which is what I was attempting in my prior post.
     
  9. Apr 8, 2010 #9

    Augment

    Augment

    Augment

    Member

    Joined:
    Apr 7, 2010
    Messages:
    22
    Likes Received:
    0
    I don't have a voltmeter, but will attempt the test tomorrow. If the fan is energized this way, does it mean the tstat is bad?
     
  10. Apr 8, 2010 #10

    kok328

    kok328

    kok328

    Well-Known Member

    Joined:
    Nov 20, 2007
    Messages:
    2,755
    Likes Received:
    249
    If the fan turns on as a result of the test, it will either be a bad Tstat or the wiring from the Tstat to the furnace.
    If you'd like, you can jumper the R & G terminals on the back of the Tstat and this will verify the wiring and result in determining a bad Tstat.
     
  11. Apr 8, 2010 #11

    Wuzzat?

    Wuzzat?

    Wuzzat?

    Well-Known Member Sponsor

    Joined:
    Jan 20, 2010
    Messages:
    2,471
    Likes Received:
    175
    I think it's somewhat more likely that the problem is at the furnace end.
     
    Last edited: Apr 8, 2010
  12. Apr 8, 2010 #12

    Augment

    Augment

    Augment

    Member

    Joined:
    Apr 7, 2010
    Messages:
    22
    Likes Received:
    0
    I looked at the furnace,don't know where to start. Jumping the t-stat seems easier. What will this tell me if the fan does go on?
     
  13. Apr 8, 2010 #13

    Augment

    Augment

    Augment

    Member

    Joined:
    Apr 7, 2010
    Messages:
    22
    Likes Received:
    0
    I tried to jump on the tstat, nothing happened with green and red. I accidentally touched red and yellow, started fan briefly then stopped (a/c mode).
     
  14. Apr 8, 2010 #14

    kok328

    kok328

    kok328

    Well-Known Member

    Joined:
    Nov 20, 2007
    Messages:
    2,755
    Likes Received:
    249
    What this tells us is that you could possibly have a bad wire from thermostat to furnace.
    You'll have to jumper the R & G terminal at the furnace and see if the blower comes on.
    Inside the furnace you'll see a wire coming in from the tstat.
    Most likely brown insulation containing multiple colored wires.
    What the thermostat does is completes a circuit of 24VAC from the R terminal to the G terminal to energize the fan circuit when fan "on".
    If the G wire is bad, then power won't make it back to the furnace from the tstat. So now we must energize the G terminal at the furnace to eliminate this possibility. Inside the furnace you'll see the brown wire and it's multi-colored wires attach to the various terminals to run heat, A/C, fan, etc.
    Touch the jumper wire to the R & G terminal and see if the fan comes on.
     
  15. Apr 8, 2010 #15

    Augment

    Augment

    Augment

    Member

    Joined:
    Apr 7, 2010
    Messages:
    22
    Likes Received:
    0
    I jumped the R & G terminals on the furnace and the fan did come on. I should mention the G and Blue wires seem to share a terminal, don't know if this means anything.
     
  16. Apr 8, 2010 #16

    kok328

    kok328

    kok328

    Well-Known Member

    Joined:
    Nov 20, 2007
    Messages:
    2,755
    Likes Received:
    249
    On which terminal are the Green & Blue wires sharing (G or B)?
     
  17. Apr 8, 2010 #17

    Augment

    Augment

    Augment

    Member

    Joined:
    Apr 7, 2010
    Messages:
    22
    Likes Received:
    0
    G terminal
     
  18. Apr 8, 2010 #18

    kok328

    kok328

    kok328

    Well-Known Member

    Joined:
    Nov 20, 2007
    Messages:
    2,755
    Likes Received:
    249
    That's curious, based on what your telling me the fan should work when switched to "On".
    We are going to have to back it up a step as I can't readily affect a repair online.
    I need to know what wires (color) are attached to what terminals on both the furnace and thermostat. Watch for crossed wires where the color and terminal does not match the opposite end (furance vs. tstat).
    Just to be sure, this is not a heat pump system; correct?
    We are definitely closing in on the problem but, I need more info to complete the picture.
     
  19. Apr 9, 2010 #19

    Augment

    Augment

    Augment

    Member

    Joined:
    Apr 7, 2010
    Messages:
    22
    Likes Received:
    0
    This is not a heat pump system, just forced air gas. I've noticed that the wires hooked up to the thermostat and then reappearing at the furnace don't match. On the thermostat there is an unattached blue wire, and attached white, yellow, green and red all attached to the correct terminals.

    At the furnace, the thermostat wires are red attached to red, black attached to Y/Y2, white attached to W/W1, blue attached to green, orange attached to nothing.

    I noticed that the green wire does not come from the tstat wires, it's in a separate bunch of wires of all colours. However, it's connected to the G terminal and there's another connection to the fan (a plug that you can pull in and out to different fan levels). Then the whole bunch leads back to the blower at the back of the furnace.

    This is getting more and more complicated I think. Thanks for your help!
     
    Last edited: Apr 9, 2010
  20. Apr 9, 2010 #20

    kok328

    kok328

    kok328

    Well-Known Member

    Joined:
    Nov 20, 2007
    Messages:
    2,755
    Likes Received:
    249
    Sorry, I forgot to ask whether there are any terminals where there are no wires attached on both the tstat and furnance ends.
    Something is definitely mis-wired on purpose or on accident.
    Not sure which is the case at this time.
     

Share This Page