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Voltage drop

Furnace in attic.No heat call.Find 7.5 fuse in control board with the smell where someone let the smokeout of the

Replace transformer.install the proper 5 amp fuse.Powerup
furnace and amp draw at the transformer was .43.
No voltage drop running steady.Check delta t,yadda,yadda.

Write invoice leave parts with customer.Two day laters she calls back with no heat again.

Arrive to find blown fuse again.Went stright to the low voltage ohm everything out all is well.Check all wiring thruout the furnace.All is well.

Install new fuse..nothing happen.Check voltage.only 90 volts

Found burner switch with the wires plug in to the back of the switch not wrap around the screws.Switch about fell apart in my hands when removing.

Install new swith with screw wrap around screws.recheck volts had 120 system firesup and all is well.

Hey sparky wrap the wire around the screw will ya.


  • Empire_2
    Empire_2 Member Posts: 2,343
    Loose connections....:-)

    These will do the same thing. As the contact points become either corroded or loose if that is the case, crazy things start to happen. Usually when you are not there. Our Maintenance sheets states, "Tightened all wire connections". You would be surprised how often this happens with 220VAC on A/C units popping breakers.

    Mike T.
  • don_185
    don_185 Member Posts: 312
    Hello Mike

    its good to have you back.Must have been busy.

    Its funny how that loose wire will have you troubleshooting
    things that are not even the problem.

    Case in point..buddy of mine calls me up on sunday and asked if I had a hsi on the truck.Sure I've got one come and get it.

    Fews hours go by and he calls backup to tell me it was not the hsi because the new one did the same thing.
    I asked what was that?He said the ignitor would glow and then go out before the gas valve open.

    His finding was a voltage drop from a loose wire.

    Them loose wire is like having one bad trap on a steam system.Makes a man chase his tail.

  • Empire_2
    Empire_2 Member Posts: 2,343
    Hi back Don, good to be back..

    CA for 3 weeks on a well deserved Vacation:-) Since my cell phone never stopped ringing, I really took too long in what I thought would be a relaxing trip.:-). I have good guy's that can cover, but every ring made my heart beat hard thinking I would have to take an early flight back.... Thank goodness.

    The best thing I have in my own service bag of tricks are my fluke meter and 3 Set's of jumpers. I can actually trouble shoot in a pinch with just the jumpers. As to your first post, I hate contactors that are not 2 pole which are "Definite Purpose" contactors meaning 2 pole 1 throw. That it where your first situation confused you a little. I have seen loads like cond. fans short to ground and run @ half speed or so. Just takes a while to figure out and understand what is happening. It's kinda like a learning curve:-)

    Mike T.
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