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Re: [Electronics_101] Re: Furnace problem - mystery deepens :-(

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  • Frank Mead
    I also had a similiar furnace problem...and having checked all the obvious maladies I pulled the printed circuit board which contains a multitude of relays and
    Message 1 of 5 , Nov 30, 2009
      I also had a similiar furnace problem...and having checked all the obvious
      maladies I pulled the printed circuit board which contains a multitude of
      relays and stuff...
      I found a burnt trace on the PCB that had become a relative large
      resistance.
      Scraping the gunk from the trace and then soldering a piece of #20 wire
      to the offending trace cured the problem...BTW, the affected relay was
      the one that controlled the fan/blower...
      I also noted that wilst putting the pcb back into it's proper place was no
      easy task...lots of push on connectors...so keep track of the placement
      of the multitude of wires.
      Frank

      On Mon, Nov 30, 2009 at 11:39 AM, sailgene <mardalee@...> wrote:

      >
      >
      > Chris,
      >
      > I don't recall whether or not you mentioned if your pilot light was firing
      > up. This is where my furnace would get to before automatically shutting
      > down. Again, if the pilot light fires up, then it's most likely the heat
      > sensor which the pilot light strikes. And that sensor is a thin wire which
      > gets oxidized or something to the point where it does not sense the heat. A
      > light and careful sanding of it may fix it.
      >
      > If the pilot light isn't turning on, then you're probably right looking at
      > the board.
      >
      > Gene Darby
      >
      > --- In Electronics_101@yahoogroups.com <Electronics_101%40yahoogroups.com>,
      > "lcdpublishing" <lcdpublishing@...> wrote:
      > >
      > > As this problem is an intermittent problem, catching it in the "act" has
      > been troublesome.
      > >
      > > Yesterday, I noticed the furnace stuck in that mode of the vent fan
      > running. I grabbed my meter and checked voltage at the switch and found no
      > voltage on either side of the switch. As I tried to investigate further into
      > the problem, I bumped something (no idea what), then the blower fan (to move
      > air around the shop) kicked in and started running without heat.
      > >
      > > I turned it off and on again and everything worked fine.
      > >
      > > Today, something similar happened. This time while investigating, I
      > nearly fell off the ladder and hit the damn power switch which reset it.
      > >
      > > I am no longer convinced the pressure switch is acting up. Rather, I
      > suspect something further up the circuit which provides 24Vac to that switch
      > is the starting point of the problem.
      > >
      > > I may have to remove the board from this thing and get a good look at it
      > and clean it up etc. It probably will help in figuring it out if I had a
      > clue what was on the board. Right now the only thing I have to work from is
      > the schematic which so far has not helped me much.
      > >
      > > Chris
      > >
      >
      >
      >


      [Non-text portions of this message have been removed]
    • dave_mucha
      Should be easy to add an LED unit with an LED on the hot before the switch. That way, you would know if there was power to it. as for the board, pull it, and
      Message 2 of 5 , Dec 1, 2009
        Should be easy to add an LED unit with an LED on the hot before the switch. That way, you would know if there was power to it.

        as for the board, pull it, and look it over for a lose connection on one of the major outputs. something like a 110VAC line or some such.

        Dave






        --- In Electronics_101@yahoogroups.com, "lcdpublishing" <lcdpublishing@...> wrote:
        >
        > As this problem is an intermittent problem, catching it in the "act" has been troublesome.
        >
        > Yesterday, I noticed the furnace stuck in that mode of the vent fan running. I grabbed my meter and checked voltage at the switch and found no voltage on either side of the switch. As I tried to investigate further into the problem, I bumped something (no idea what), then the blower fan (to move air around the shop) kicked in and started running without heat.
        >
        > I turned it off and on again and everything worked fine.
        >
        > Today, something similar happened. This time while investigating, I nearly fell off the ladder and hit the damn power switch which reset it.
        >
        > I am no longer convinced the pressure switch is acting up. Rather, I suspect something further up the circuit which provides 24Vac to that switch is the starting point of the problem.
        >
        > I may have to remove the board from this thing and get a good look at it and clean it up etc. It probably will help in figuring it out if I had a clue what was on the board. Right now the only thing I have to work from is the schematic which so far has not helped me much.
        >
        > Chris
        >
      • James Elliott
        Broken solder joints on a PCB, lose wiring harness, lose screw holding a wire to a terminal, or faulty switch would be my guess since it seems to turn on after
        Message 3 of 5 , Dec 4, 2009
          Broken solder joints on a PCB, lose wiring harness, lose screw holding a wire to a terminal, or faulty switch would be my guess since it seems to turn on after a bump. Sounds like a 'mechanical' issue in the circuit somewhere.. I would check the human interfaces as well as the stuff that is connected on something that moves/vibrates, and then check further down the line from the device that moves/vibrates (i.e. maybe the movement/vibration pulled something at the 'other' end).

          Jim



          ________________________________
          From: lcdpublishing <lcdpublishing@...>
          To: Electronics_101@yahoogroups.com
          Sent: Sun, November 29, 2009 2:53:37 PM
          Subject: [Electronics_101] Furnace problem - mystery deepens :-(


          As this problem is an intermittent problem, catching it in the "act" has been troublesome.

          Yesterday, I noticed the furnace stuck in that mode of the vent fan running. I grabbed my meter and checked voltage at the switch and found no voltage on either side of the switch. As I tried to investigate further into the problem, I bumped something (no idea what), then the blower fan (to move air around the shop) kicked in and started running without heat.

          I turned it off and on again and everything worked fine.

          Today, something similar happened. This time while investigating, I nearly fell off the ladder and hit the damn power switch which reset it.

          I am no longer convinced the pressure switch is acting up. Rather, I suspect something further up the circuit which provides 24Vac to that switch is the starting point of the problem.

          I may have to remove the board from this thing and get a good look at it and clean it up etc. It probably will help in figuring it out if I had a clue what was on the board. Right now the only thing I have to work from is the schematic which so far has not helped me much.

          Chris







          [Non-text portions of this message have been removed]
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