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  1. #1
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    Jan 2014
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    Why do manufacturers mount control board in the air stream?

    Why are they almost always mounted next to the blower, which is likely to have micro vibrations, and in the return air stream?

    An exposed circuit board, especially modern ones with low voltage components and very tight traces, should be enclosed in air tight enclosure. Those boards have nothing on them that generates heat. Why mount them where they are exposed to an air stream and vibration?

  2. #2
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    Nov 2008
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    Piney Flats, Tn.
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    where else do you propose for them to put them? Next to the burners, hot inducer? Outside of the cabinet?

  3. #3
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    Jan 2014
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    Trane seems to have done a little better job on this unit.

    I was looking at some modern communicating condensers with variable speed, and their circuit boards look very advanced. Not through hole components and tracks 1/8" apart. Surfaced mounted components with very close tracks. Not unlike a modern computer motherboard.

    On the condenser it is even worse, the board will be outside, exposed to humidity and constant temperature swings, with spider webs all over it in a month. I just can't imagine how it would last.
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  4. #4
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    Aug 2002
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    Don’t get me started how many boards I have seen failed from that design trane uses.

    They have an issue with the inducer leaking water right down on the board. These are almost brand new systems, imagine the problem when the seals actually get some wear and see how many boards are failed.

    See very few boards failed in blower compartments that are not caused by other issues. Mounted on the blower in the airflow have never been an issue.

  5. #5
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    Jan 2004
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    Quote Originally Posted by BillDX View Post
    Why are they almost always mounted next to the blower, which is likely to have micro vibrations, and in the return air stream?

    An exposed circuit board, especially modern ones with low voltage components and very tight traces, should be enclosed in air tight enclosure. Those boards have nothing on them that generates heat. Why mount them where they are exposed to an air stream and vibration?
    They have relays on them. The coils of the relays generate heat when they are energized.

    Being in the air stream they are kept both cool in the summer, and warm in the winter.
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  6. #6
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    Jan 2014
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    Quote Originally Posted by beenthere View Post
    They have relays on them. The coils of the relays generate heat when they are energized.

    Being in the air stream they are kept both cool in the summer, and warm in the winter.
    Don't want those relays catching a cold in the winter. I'm 99.99% sure your comment was a joke.

  7. #7
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    Quote Originally Posted by BillDX View Post
    Don't want those relays catching a cold in the winter. I'm 99.99% sure your comment was a joke.
    You really want those electronics to be at Temps over 160°F?

    Or at Temps below -20°F?
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  8. #8
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    Mar 2018
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    Chico, Ca #StateofJefferson
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    The boards are full of resistors and the silicone will brown around them with age, so they do produce heat. That stupid trane design pretty much ensured that the blower motor, wheel and run cap were never checked on PM's. Usually these days the boards are dipped to prevent condensation damage, although it doesnt help any connector plug-ins to the board

  9. #9
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    Jan 2014
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    Quote Originally Posted by beenthere View Post
    You really want those electronics to be at Temps over 160°F?

    Or at Temps below -20°F?
    But they are anyway when the blower is not running. It's not like the board is un-powered when the system is not running. If anything, constant temperature cycling is more detrimental to a circuit board. 125C (257F) rated board components are a dime a dozen. Very common in automotive. More than likely the HVAC standard also.

  10. #10
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    Jan 2004
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    Quote Originally Posted by BillDX View Post
    But they are anyway when the blower is not running. It's not like the board is un-powered when the system is not running. If anything, constant temperature cycling is more detrimental to a circuit board. 125C (257F) rated board components are a dime a dozen. Very common in automotive. More than likely the HVAC standard also.
    Control board in an attic furnace is near room temp unless their is a power failure, or other failure that causes the unit not to run for several hours.Other wise, conditioned air is moving through the blower compartment even when the unit isn't running.

    RTUs usually have the control board mounted where air movement from the indoor blower, or condenser fan helps keep it somewhat cool.
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  11. #11
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    May 2000
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    Indianapolis, IN, USA
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    That Trane is a joke for return air. Only a 14x18 opening. Most guys seem to slap a filter against that so instead of 16x25 worth of filter get get so much less. Our supplier has transitions custom made to go from the small opening to a 16x25 media cleaner. For bigger furnaces, a 6" box for under and a transition from box & small opening to 20x25 media cleaner.

  12. #12
    Join Date
    Oct 2014
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    Saint Pail, Minnesota
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    My Armstrong has the board mounted on the side of the inducer cabinet. I love it. It’s a taller unit so there is certainly more room and it is located away from any leaks.

  13. #13
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    Mar 2018
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    RTU's are a bit over 25% of the equipment in my area but only account for ~5% of the boards I replace. I always figured this was due to the much lower amp draw going thru the relays than on a 115v furnace. Most of those relays are barely rated for the motors FLA, let alone startup current

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