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  1. #1
    Join Date
    Nov 2005
    Location
    Ohio
    Posts
    10
    Hello all.

    I am new to the site. I am currently an industrial commercial HVAC tech. I am also an adult instructor at a local vocational school, the class: introduction to residential HVAC.

    I wanted to get some industry pros opinion on the best method for heat pump lock out for dual fuel systems i.e. indoor coil located above the heat exchanger.

    For example: Independent outdoor temp sensor to lock out the HP.

    White Rogers series 90 or other variation, internal lockout, upon W2 engagement after 1 minute.

    Independent dual fuel relay kit. Consists of three double pole double throw relays. Immediately locks out HP with W2 engagement

    My top choice would be the relay kit, but it is an extra expense for the customer.
    The T-stat lock out is great but it waits a whole minute to lock out the HP. Too long IMO.

    So what is your opinion?

    I apologize for the misspelling in the title I can't seem to edit it.


    [Edited by journeymen on 11-11-2005 at 10:59 AM]

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,338
    We usually use the dual fuel stats like the high end W-R or the Vision Pro. Personally I have a DPDT relay that opens Y and energizes W1 on the gas furnace. I have no outdoor stat, just use emergency heat setting if I don't want the pump on.

    The Vision Pro shuts off the pump right away, unlike the minute the W-R takes.

  3. #3
    Join Date
    Jun 2003
    Location
    Florida
    Posts
    9,548
    I'd go with the relay as they shouldn't be on together, even for 1 minute, IMO.
    If everything was always done "by the book"....the book would never change.

  4. #4
    Join Date
    Nov 2005
    Location
    Ohio
    Posts
    10
    Originally posted by BaldLoonie
    We usually use the dual fuel stats like the high end W-R or the Vision Pro. Personally I have a DPDT relay that opens Y and energizes W1 on the gas furnace. I have no outdoor stat, just use emergency heat setting if I don't want the pump on.

    The Vision Pro shuts off the pump right away, unlike the minute the W-R takes.
    Just curious, how do you configure a single DPDT relay to lock out your HP.

    What happens when the HP goes into defrost, will it not energize the relay and lock out the compressor?

  5. #5
    Join Date
    Jul 2000
    Location
    DeFuniak Springs, FL
    Posts
    990

    I just set one of these up yesterday (11-11-05)

    I don't see a problem energizing the gas furnace during the defrost cycle of the heat pump. Anyone disagree? and most importantly why? Used the Vision Pro 8000 and outdoor sensor for the dual fuel control. I can understand the reasoning for not running the heatpump and furnace at the same time, figuring that if this happens my Rheem high pressure switch will come into play.
    Randy Yates

  6. #6
    Join Date
    Jan 2003
    Location
    Kentucky
    Posts
    2,651
    we use touch tone stats,with outdoor sensor...R410A systems,we lock out the HP at 25 degrees,and R22 systems at 30 degrees...seems to work pretty well with the temps.,here in KY...we always set up in the restricted mode...if the furnance and heat pump are allowed to run at the same time,high pressure switches at heat pumps can easily trip,and have found alot of leaking indoor coils,on dual fuels,where set up in the unrestricted mode...this puts alot of stress on the coil and can cause it to bust/leak...i have not seen any problems with the gas furnance on in the defrost mode,if wired correctly

  7. #7
    Join Date
    Feb 2004
    Posts
    2,597
    why lock out 410 at 25 deg. and 22 at 30 deg.?

    seems to me the refrigerant type isn't an issue on lock out temps.

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