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  1. #1
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    Smart/As needed evap defrost?



    All, Are there any "smart" defrost controls that can sense when a low temp evaporator needs to be defrosted?

    It seems to me a air pressure differential system between the front and back of the coils could be used to trigger an as needed defrost cycle rather than simply using a regularly scheduled time clock.

    In my case, the humidity loads on my evaporators can change significantly with production demands. If possible, I'd rather not pump heat into a freezer to defrost a unit if not needed.

    Thanks!



  2. #2
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    Re: Smart/As needed evap defrost?

    Hi, sounds like your talking about defrost air switch maybe, it's something I come across quiet regular on transport fridges. The way I have seen it done is the air switch is usually located outside the load space with two 1/4inch rubber pipes running from the switch to the evap, each pipe is run to two plastic air funnels, one at air on and one at air off. When you get a plugged coil, the pressure differential switches the air switch putting the unit onto defrost. Defrost termination is taken care of by a temperature klixon mounted on the evap coil somewhere. You may have to put the evap fans on a timer to stop warm air being blown out when it comes off defrost or I guess you could use another temperature klixon to switch evap fans back on when evap temp is at a suitable temperature perhaps. I am sure a system could be devised with a little cunning if there is not one commercially available already.

  3. #3
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    Thumbs up Re: Smart/As needed evap defrost?

    Alpha,

    BINGO! Once I knew the name of it, was easy to find.

    White Rogers makes an Air Switch rated down to -40 degrees, well within the temps my freezers are maintained at.

    I'm sure there are others and along with a couple simple timers and relays, I can easily achieve an as-needed defrost.

    I think the hardest part will be pulling some new wiring through the existing conduit to get control/sensor trigger from the evaporator to the controls.

    From there it'll be a simple matter to adjust the differential switch to trigger correctly.

    Many thanks!

  4. #4
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    Re: Smart/As needed evap defrost?

    Kuba make a defrost on demand refrigeration controller. It needs special temperature sensors and a Kuba evaporator. Those who use it, say that it works.

  5. #5
    Cyborg-mechanic's Avatar
    Cyborg-mechanic Guest

    Re: Smart/As needed evap defrost?

    in my experience and and to my knowledge and skills, all you need is a pressure switch,

    if the right amount of gas in the system and the condensor's clean and everyhing is working well

    you are sometimes provided with a evap temp to room temp relevance,

    the pressure senses this temp, and if the evap temp is right let's say the lp is running at 38 pounds on R22 then the evap temp is about -20, to my knowledge, and if the evap is -20 and the system runs and runs because the smart donkey that did the installation didn't install a pressure switch on a hot day or a day when the fridge system is used alot, the evap will start icing up, then you will have endless problems trying to sort it out by getting extra unneeded devices to sort it out' here's your answer

    Get a pressure switch and install it, and take that timer out and sell it to the scrap or set it to go off twice 3 times a day for 45 minutes so that the comp can cool down just incase,

    from my knowledge, so now, if the evap is at -20 and it has reasonbly good condensing, the room will go down to -14 in about 60 minutes, with no load it will go down to -18 or even -20 in about 15 minutes or less,

    please correct me if i made any mistakes,

    my regards.
    Cyborg-mechanic

  6. #6
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    Re: Smart/As needed evap defrost?

    Used to use a defrost on demand system . But not around any more took a bit to set up right but worked ok in the end . It ran on a evaporator temp probe . Called coolguard a local company in the north east of england

  7. #7
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    Re: Smart/As needed evap defrost?

    so many ways and so many systems available, just Google and be happy.

    Ice

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