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  1. #1
    Join Date
    Jan 2005
    Posts
    56
    I had a call on a Carrier furnace 58SE175-3. How do I tell if the flame sensor is bad? I can't recall how to set my multimeter to test it. The problem is the over temp is shutting burners down before blower comes on. Any ideas?

  2. #2
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,038
    I never check the flame signal on one of those. You need to look real close at the dimples. Look for rusted lines around them.

    I'd guess just put the flame sensor in series with your meter.

  3. #3
    Join Date
    Apr 2004
    Location
    Niantic, Illinois
    Posts
    545
    Yes, you put your meter in series between the flame senser and the wire that attaches to the flame senser. Set your meter for microamps and fire unit.

  4. #4

    I had...

    ...a problem like that before and found the vent cap collapsed where a roofer tried to use it for a stool

  5. #5
    Join Date
    Jan 2005
    Location
    Central Fl
    Posts
    49
    I'm not positive if that particular model is sensing flame by rectification (single wire going to little bar in the flame), but from what I've read so far, it seems it probably does.

    To test, you set your multimeter to microamps DC. Your meter has to be in series with the flame sensor. You will usually read anywhere between 2-8 uADC on your meter when the flame is enveloping the rod. Most controls need to see between .5-1 uADC for flame sensing.

    In other words, the control board is looking for the amperage, or flow of current, to sense a flame. This is completely different than a thermocouple which does actually generate millivoltage to hold a magnet in place to keep the gas valve open.

    By the way, as the flame sensor gets "dirty", the microamperage will decrease. A brand new furnace will usually, in my experience, generate 5-7 uADC. When you see it dropping dangerously close to the 1 uADC minimum, you might want to try clean the rod.

    [Edited by gatorguy on 01-29-2005 at 12:45 AM]

  6. #6
    Join Date
    Feb 2004
    Posts
    2,478
    uA not MA is microamps I sure you already new that.

  7. #7
    Join Date
    Jan 2005
    Location
    Central Fl
    Posts
    49
    Good Call. Must have been a Friday night after a 65 hour week when I was typing that I corrected my mistake. Thanks.

  8. #8
    Join Date
    Nov 2001
    Location
    Moose Jaw, Saskatchewan, Canada Occupation:Interprovincial Plumber, Commercial Gasfitter Interests:
    Posts
    2,414
    What does a high limit problem have to do with flame signal?????????????????
    I love my job, but paydays Thursday

  9. #9
    Join Date
    Jul 2004
    Location
    midwest
    Posts
    2,868
    Originally posted by rich pickering
    What does a high limit problem have to do with flame signal?????????????????
    I was thinking the same thing but im not a Carrier guy so I kept quiet.

  10. #10
    Join Date
    Jan 2005
    Posts
    56
    Sorry, the flame sensor was just a question. The high limit was the problem. It kind of ran together!! It's been a bad week.

  11. #11
    Join Date
    May 2001
    Location
    Kansas City
    Posts
    2,729

    Re: I had...

    Originally posted by airmechanix
    ...a problem like that before and found the vent cap collapsed where a roofer tried to use it for a stool
    That would trip the high limit on the flue draft. Are you in KC?

  12. #12
    Join Date
    Nov 2003
    Location
    carpentersville IL
    Posts
    24
    I'm not sure what type of furnace this is either but to start, if it is a counterflow, make sure your filters are clean. Not enough return air and your limit will trip. Circuit board could be malfunctioning and not starting fan in time. If there is no circuit board whatever controls the fan may not be working properly. Thermostat heat anticipator fried or set wrong, limit switch malfunctioning. Check temp at limit when it shuts down. Good luck

  13. #13
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,038
    Isn't that a old green monster with a damper in the flue?

    I think they had a cam stat style of limit and a G60 control on the gas valve or mounted above the burners.

    When I suspected a flame signal problem I would just clean the flame sensor and fire it up.

    If the limit is triping you might try to stick a probe in place of the limit and see how hot it's getting. Could be a bad camstat. I rember replacing more that I thought I should have the last couple of years I work for that Carrier dealer. Seemed like poor quality.

    Those furnaces had a coating in the HX. Look close for any rust lines. They could be cracks. Look hard at the dimples and water test if possible.

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