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  1. #27
    Join Date
    Nov 2011
    Location
    St. Louis
    Posts
    2,940
    Quote Originally Posted by Gerbs1983 View Post
    We actually did that on this one. Took 24 v from board to valve, fired gv and ran without issue. Allowed us to rule out any issue w gas valve. First time I have done this, it also allowed us to run furnace long enough to trip roll out for good, leading to the root issue.
    How exactly? You cycled normally and added another 24v to the GV, in addition to the 24v it might already be getting?

    Or did you remove the existing wires from the GV? If so, how was the circuit completed?

  2. #28
    Join Date
    Feb 2013
    Location
    Champaign, IL
    Posts
    23
    Removed existing wires from gas valve. Used jumper from r and jumper from common. Once board gave call for gv, manually gave gv 24v from terminal block on board.

    Not sure if this is a good thing or a bad thing, but it worked. Allowed us to rule out gv and find the real problem. Also able to determine gas pressure.

  3. #29
    Join Date
    Nov 2011
    Location
    St. Louis
    Posts
    2,940
    Quote Originally Posted by Gerbs1983 View Post
    Removed existing wires from gas valve. Used jumper from r and jumper from common. Once board gave call for gv, manually gave gv 24v from terminal block on board.

    Not sure if this is a good thing or a bad thing, but it worked. Allowed us to rule out gv and find the real problem. Also able to determine gas pressure.
    I guess it's fine if the GV relay and GV are on their own little circuit. I just grabbed the nearest Carrier schematic I have and it appears the pressure switch has a way back to common thru the CPU, so that unhooking the GV wires would not effect the rest of the cycle. I never bothered to notice whether most furnaces are likewise wired, always assumed all the safeties were wired in series with GV to shut it down if one opened.

  4. #30
    Join Date
    Feb 2013
    Location
    Champaign, IL
    Posts
    23
    True, on this particular Trane, the board controlled gas valve on its own mini circuit, per the 12 pin plug.

  5. #31
    Join Date
    Feb 2013
    Location
    Huntsville, AL
    Posts
    76
    Great idea, disconnecting existing wiring on the valve and running a 24 and common off the low voltage coming in, basically bypassing the board control, then testing the opening of the valve by the outgoing pressure..Thanks!

  6. #32
    Join Date
    Feb 2013
    Location
    north georiga
    Posts
    478
    Quote Originally Posted by uniservice View Post
    This is one of the times that an old analog meter will be better at checking the valve input than a digital.
    thats why my simpson is still on the truck and the guys i work with know to keep their hands off of it!!!

  7. #33
    Join Date
    Feb 2013
    Location
    north georiga
    Posts
    478
    encountered a similar problem (on an l.p. gas system) and found it to be the second stage regulator locking up as soon as there was a slight drop in pressure,

  8. #34
    Join Date
    Mar 2012
    Location
    West Chester, PA
    Posts
    511
    could be bad solenoid coil in valve, weak transformer, voltage drop across pressure switch (check w/ volts not continuity), overloaded transformer (disconnect all peripherals and jump unit out at IFC)

  9. #35
    Join Date
    Mar 2012
    Location
    West Chester, PA
    Posts
    511
    If the PS is in series to the gas valve, then my money would be on a volt or 2 drop across that switch

  10. #36
    Check if it properly grounded,than check gv valve.

  11. #37
    Join Date
    Nov 2011
    Location
    Philadelphia, PA
    Posts
    195
    Quote Originally Posted by ComfortablyNumb View Post
    I'm still saying bad valve...

    Or maybe a grounding issue.

    Also just remembered - disconnect the power supply and check for voltage between neutral and ground. Shouldnt have more than 0.5vac if so you may have a neutral/grounding issue. It's put an end to me banging my head against the wall before... on a Trane 90% if I remember correctly. Read between 15-25v while also getting 95-105v hot to ground.
    I've measured up to 10 volts to neutral in the past. I thought this was just feedback. Could this be a clue that there is a problem?

  12. #38
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,032
    If if you or anyone else has 10 volts between the neutral and the equipment grounding conductor, you've got some work to do there my friend.

  13. #39
    Join Date
    Mar 2001
    Posts
    1,455
    X2
    One way to outthink people is to make them think you think. They'll think you're not really thinking what you're trying to get them to think you think...........

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