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    jimmyleejon's Avatar
    jimmyleejon Posts: 8, Reputation: 1
    New Member
    		  
    #1

    Nov 30, 2008, 10:50 AM
    Relays to stop humidification HVAC
    How do I wire a relay in to stop humidification during a call for cooling also how do I wire a cooling system up to a old furnace using a fan centre the old furnace only has a fan limit
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #2

    Nov 30, 2008, 01:20 PM

    In both cases: Heatpump or conventional?

    2nd case: one or two speed blower? How is the blower controlled? In the old days, the system was heat only single speed. As part of the upgrade a two speed blower was installed.
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #3

    Dec 2, 2008, 06:53 AM
    I believe he is trying to bypass the circuit board and all the safetys. Not good.
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #4

    Dec 2, 2008, 12:04 PM

    I'm just wondering if it's one of those relics where you have a summer/winter switch that controls the fan and the motor HP is like 1/3 instead of 1/2 and no G terminal. AC or humidifiers were not even thought of before the time.

    Even this isn't quite enough: How to Install and Wire the Honeywell L4046B combination Furnace Fan Limit Switch Control: a guide to the fan limit switch installation and electrical connections - Honeywell L4064B Combination Fan and Limit Switch

    When a two speed fan is involved.

    In reality, you need to look at:
    1. Is the fan on (Note 1)?
    2. Is there a call for heat?
    Then enable humidifier

    This is tough when there is no low/high speed fan to begin with and it's added.

    Usually there is a third pole that can be used/added on fan centers for EAC's and humidifiers.
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #5

    Dec 2, 2008, 01:12 PM

    I forgot about this method as described here:

    http://www.ontimemall.com/aprilaire-...ers-manual.pdf

    You can use a current sensing relay to determine whether the fan is on. It's also easy to determine if in heat mode and fan is on.

    24 VAC Power is between C&W if you have a call for heat, but fan may not be running.

    If you put a current sensing relay on the low speed of the fan combined with the internal humidistat, you should be fine.

    There is lots of little nuances that can cause grief.
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