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  1. #1
    Join Date
    Oct 2006
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    Question for you control experts, typically on a split system heat pump is the AHU wired such that the AHU turns off when the outside unit goes in to defrost mode?? It seems to me that it would, but have never had much concern about this issue.

    Thanks in advance..

  2. #2
    Join Date
    Oct 2005
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    No, The AHU is actually absorbing heat from inside so it can more efficiently reject the heat outside to melt any ice off(refrigeration at work). If AHU is off, there is less heat transfer across inside coil, so 1)it takes longer to defrost 2) you may freeze coil inside... Of course nobody likes to feel cold air on them when this (defrost)is happening. Thats where supplemental heat comes into play via electric heaters. The outside fan DOES need to stop while in defrost though. That way it removes the ice as quickly as possible by concentrating heat locally. Depending on which part of the country you are in (most new)defrost boards have a setting for how frequently it checks to do defrost(30-45-90min). It will check for both time and temperature initiation. and for termination of defrost it will do it on either time or temperature..This is just a quick summary of (most new)defrost...There is other types of defrost...Hopefully this helps.. Heatpumps101

    [Edited by ddcfan on 10-27-2006 at 11:23 AM]

  3. #3
    Join Date
    Mar 2003
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    in most cases supplemental heat is energized during defrost.

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