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Frost free / Auto defrost?

Discussion in 'Electronic Repair' started by Terry Pinnell, Aug 9, 2004.

  1. As our current unit is plainly struggling, I'm about to buy a new
    frost-free combination fridge/frezer. But I'm confused about one
    feature that is offered on some models and not others, namely
    'Automatic defrost'. If the product is frost-free, then why would I
    ever need to 'defrost' it? And I've seen posts which seem to imply
    this feature is undesirable, and that manual defrosting is preferable.
    The more I read, the more hazy the issue becomes!

    Any crisp and clear advice on this would be greatly appreciated
    please, as I need to place an order fast.
     
  2. Don Pearce

    Don Pearce Guest

    Frost free and automatic defrost are as far as I know the same thing.
    I have one of these, and the freezer element is a flat vertical plate
    at the back of the top cabinet. During the non-cooling phase the ice
    melts to allow any excess to drip away through a pipe onto the
    condenser bulb at the bottom, from which it evaporates into the room.

    Mine has been working fine for many years.

    The actual freezer bit at the bottom enjoys no such features, but it
    only gathers frost when I have the thing too full and the door fails
    to close properly. There is nothing for frost like a 1mm gap in the
    door seal.

    d

    Pearce Consulting
    http://www.pearce.uk.com
     
  3. Ken Weitzel

    Ken Weitzel Guest

    Hi...

    It's frost free because it auto defrosts :)

    The upside is that you never have frost problems...

    The downside is that energy consumption is slightly
    increased (the fridge shuts down two or three times a
    day and turns on a little electric heater to melt the
    ice for a few minutes)

    Ken
     
  4. Don, Ken: Thanks both. Apprecaite the fast replies. But I don't see
    how to square that with the fact that all the products I've researched
    today seem to show these as two *independent* features. That's the
    cause of my confusion.

    For example, the HOTPOINT FFA70P at
    http://www.comet.co.uk/comet/html/cache/30_823026.html
    has Frost Free AND Automatic fridge defrost.

    But the Bosch BOSCH KGU34124GB at
    http://www.comet.co.uk/comet/html/cache/30_202096.html
    has Frost Free but NOT Automatic fridge defrost.
     
  5. Derelict

    Derelict Guest

    I have seen two systems at work in modern fridges. One is the heated
    defrost (auto defrost). The other is sucking the humid air out of a
    freezer every time you close the door (frost free). Make sense?
     
  6. Don Pearce

    Don Pearce Guest

    How do they do that? The air sucked out must be replaced by -
    presumably - dry air. Where would that come from?

    d

    Pearce Consulting
    http://www.pearce.uk.com
     
  7. Julie

    Julie Guest

    No, it creates a partial vacuum. The sound of these freezers is very
    distictive -- you hear a sucking sound when you close the door.
     
  8. Don Pearce

    Don Pearce Guest

    Are you sure? To be of any use, a partial vacuum would have to be at
    least, what? 4psi below atmospheric? Now my fridge door is about 20
    inches by 30. That is 600 square inches. Multiply that by 4psi, and it
    would take a pull of 2,400 pounds to open the door.

    No.

    d

    Pearce Consulting
    http://www.pearce.uk.com
     
  9. Ken Weitzel

    Ken Weitzel Guest

    Hi Don...

    And that would most likely require seals made by NASA - else
    the vacuum would leak down quite rapidly anyway...

    I have a stand alone chest freezer in the basement... if
    you open it to get something, close it, change your mind
    and try to open it again - you can't. For a very few
    minutes.

    In my humble opinion, just a sales gimmick...

    Take care.

    Ken
     
  10. Joerg

    Joerg Guest

    Hi Ken,
    And that is often done with a lowly electro-mechanical timer. Probably
    because it is still a few cents cheaper than electronics. After all, a
    CD4060 costs north of 10 cents which would put a dent in the profit
    margin on a $1000 fridge/freezer :)

    Regards, Joerg
     
  11. Still hoping to get that!
     
  12. Gareth

    Gareth Guest

    My freezer (which is not frost free) does that as well. I think it's
    just the warm air which entered the freezer cooling down and contracting.


    --
     
  13. I read in sci.electronics.design that Joerg <[email protected]
    In mine, the heater is just wired across the thermostat contacts: COOL
    XOR HEAT at zero cost.
     
  14. Julie

    Julie Guest

    I was speaking empirically, and not technically, my bad. It looks like I'm
    wrong on my assumptions -- I retract my statements.
     
  15. We have three fridge/freezers Terry (don't ask why,
    because I don't know).

    Two of them are Hotpoint "frost free", and really not
    worth the extra money and running costs. Overload
    them just slightly, (which hampers the internal air
    circulation), and the fridge compartment freezes up
    (literally, a solid block of ice), whilst at the same
    time everything in the freezer section starts to melt.

    Don't bother with frost free.

    The third is a Bosch auto-defrost, which works very well.

    However I should have bought the more expensive Bosch,
    which has separate compressors and thermostats for the
    fridge and freezer compartments. That type works better
    over a wider range of ambient temperatures.
     
  16. But unless I've missed something, I've still not had answers to my
    original questions. To recap:

    1. Are 'Frost Free' and 'Auto Fridge Defrost' independent features
    (not 'the same thing' as Ken and Don both said)? The evidence of my
    research, as per the examples I gave, appear to imply that they are.

    2. Why is 'defrost' necessary, if the unit is frost free? Is it just
    an admission that the Frost Free thing doesn't always work?

    3. Is 'Auto Fridge Defrost' a worthwhile feature?
     
  17. Thanks, Tony. On the basis of that, plus the fact that our current
    ailing Hotpointo suffered identical problems to those you describe,
    I've just ordered a Bosch.
     
  18. John Miller

    John Miller Guest

    Yes.

    Terry --
    While I cannot answer your first two exact questions authoritatively, I
    would be willing to wager almost any amount that no refrigerator will be
    frost free without use of an auto defrost feature.

    --
    John Miller
    Email address: domain, n4vu.com; username, jsm

    He is not only dull himself, he is the cause of dullness in others.
    -Samuel Johnson
     
  19. It's not only the cost of a CD4060. Add in the power supply and other
    low power components for it (a few cents) and the power relays needed to
    switch the compressor circuit and heater circuit.
    So you heat your food when the compressor isn't running? That forms
    an oscillator with a frequency dependant on ambient temperature and
    the quality of the fridge's insulation. :) I guess what you mean is
    that it defrosts until another thermostat says there isn't any more ice.

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  20. Fred Bloggs

    Fred Bloggs Guest

    No refrigerator in the world will operate without frost if you block the
    drain for the frost water with debris and/or scum formation:) Those UK
    refrigerators you cited would be considered miniature doll-house
    accessories in the US- absolutely tiny. How cramped are the quarters in
    that country anyway?
     
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