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  1. #1

    Nordyne (Westinghouse) Dual Fuel HP/NG Defrost cycle

    I have a 2 year old Nordyne (Westinghouse) Dual Fuel furnace. Heatpump / Natural gas.
    FG7TC 100D-VC 2 stage variable speed blower furnace - - - 4 ton coil - -
    FT4BF-048ka 2 stage 16 seer heatpump with Copeland scroll compressor
    Honeywell visionpro iaq thermostat. (Controls mounted in attic by furnace)

    Problem:For two winters (going on three) the defrost cycle sends ice cold air drafts through the house. The furnace does not cut on when the heatpump is in defrost. Because of this cold draft, I have configured the thermostat to lock the heatpump out at 40 degrees F to avoid defrosts. Sadly, at an outdoor temp of 17F, the heat pump still does a fair job of heating.

    My installer states that it is running as designed during defrost mode. However, I have read many other posts where the defrost cycle and heat pump run at the same time.

    Question: For my particular unit, Should the furnace cut on during the defrost cycle? If so, is there a document I can refer my installer to?

    Thanks!

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,307
    Yes the furnace should run during defrost. Don't know of a document that says so specifically for all brands.
    Contractor locator map

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    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,323
    Controller malfunction ... board, relay or wiring. Problem is to determine which 1 /
    when will a different service tech from the installer be there?

    Intermittent problems are very frustrating for all parties.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,323
    HVAC 101 Manual


    During the 2-to-10-minute defrost cycle, auxiliary heat takes over, reducing the heat pump's overall efficiency up to 10 percent. The two most common types of defrost controls are time-temperature and demand-defrost. Time-temperature defrost controls activate defrost at regular time intervals for set time periods, whether there is ice on the outdoor coil or not. A demand-defrost control senses coil temperature or airflow through the coil, and only activates defrost if it detects the presence of ice. Obviously, choosing a heat pump with demand-defrost will pay a significant efficiency dividend.

    http://www.ferrinsairforce.com/index...kfaq&Itemid=22
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  5. #5
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,323
    HVAC 101A Manual

    http://www.achrnews.com/articles/und...e-of-operation

    Go to
    DEFROST CYCLE

    Going back to the
    Basics and Sequencing
    never hurts any1 in the troubleshooting process.

    Electrical # 5. The defrost relay powers the heat relay to bring on the indoor electric heat.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,307
    He doesn't have electric heat. need something that says gas heat.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  7. #7
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,713
    some companys do not wire dual fuel systems to run the furnace during defrost for fear of tripping a high pressure switch .i would want it wired to run and would also want a bonnet sensor in the supply
    We really need change now

  8. #8
    Thanks for all of the replies and info. I am going to call my installer and let them know that I feel the furnace should be on first stage during defrost mode. I did look at some nordyne documentation, but I cannot see anywhere where it states in wiring for the furnace to run during defrost.But, then again, I didnt see where it stated that it should not run during defrost. The Visionpro IAQ does not have any settable options regarding defrost. I am guessing defrost is controlled by the board at the compressor. I do know that it only defrosts on Ice buildup only. I know it sounds dumb, but even if the gas only fired for part of a defrost (albeit condensation may be a concern), it would be better than getting woken up at night with an ice cold draft.

    Thanks everyone for your answers!

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