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Diesel_Camper's avatar
Diesel_Camper
Explorer
Jun 28, 2015

Fan in Refrigerator question...

Hey all,

I just replaced the cooling unit in our Domestic RM 2852 and while the frige was out I decided to wire in a computer fan to blow air into the fins of the refrigerator section. I quickly found that with the fan on, the refrigerator won't go below 40f. With the fan off it will get down to freezing depending on where you move the thermistor.

My only thought on this is the fan motor is making heat, but my calculations for a .15 amp fan at 12 volts is just under 3 watts. That doesn't seem like it should be enough to overwhelm a new cooling unit. Freezer back wall stays about -10f.

What am I missing? Everyone says increase your efficiency with a fan but my fridge doesn't work well at all with one.
  • SCVJeff's avatar
    SCVJeff
    Explorer
    Jul 01, 2015
    Old-Biscuit wrote:
    The best way to get accurate temp measurements is by using a thermometer in a glass of water.

    Shooting temps with an IR gun will only give you surface temp where you point IR beam......not fridge air temps

    You CAN measure fin temp....it is roughly 10*F colder then air temp

    But a glass of water in various places in fridge with thermometer will be more accurate
    now I feel better. Mine is a probe sealed in a water bottle, but I thought it was too anal, and is a good day between measurements.
  • Diesel_Camper's avatar
    Diesel_Camper
    Explorer
    Jun 30, 2015
    My temps above are based on a thermometer inside a soda can of water on the upper door shelf.
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Jun 30, 2015
    The best way to get accurate temp measurements is by using a thermometer in a glass of water.

    Shooting temps with an IR gun will only give you surface temp where you point IR beam......not fridge air temps

    You CAN measure fin temp....it is roughly 10*F colder then air temp

    But a glass of water in various places in fridge with thermometer will be more accurate
  • SCVJeff's avatar
    SCVJeff
    Explorer
    Jun 30, 2015
    Take an IR reading in several different places in the box without the fan, I'll bet its not consistent. The point of the fan is simply to make it consistent everywhere.
    Too much fan heat? I doubt it. External box thermocoupling is probably x10+ times that.
    You don't need allot of volume to move the air around. 150ma is not a big fan at all.
    Move the fan away from the thermocouple, as in turn it 180 degrees and see how that is.
  • Diesel_Camper's avatar
    Diesel_Camper
    Explorer
    Jun 30, 2015
    Yes I'm here. I can now say difinitively that my refrigerator gets far colder without the fan. My only thoughts are the fan itself is making too much heat. An overnight run with the fan will hit 38f. An overnight run without will hit 34, and depending on where the thermistor is, below freezing. I have a 12v .15 amp CPU gan which looks smaller that the off the shelf fin fans.
  • SCVJeff's avatar
    SCVJeff
    Explorer
    Jun 29, 2015
    Vulcan Rider wrote:
    SCVJeff wrote:
    "Necessary" is a matter of opinion and you are far into the minority on this one.


    In the minority of what exactly ??

    Are you saying that you believe that over 50% of RV owners waste their money on a refrig fan that they don't need ??---snip---
    exactly the opposite. Any box fan that can circulate within the box will make it more efficient.
  • Vulcan_Rider's avatar
    Vulcan_Rider
    Explorer
    Jun 29, 2015
    SCVJeff wrote:
    "Necessary" is a matter of opinion and you are far into the minority on this one.


    In the minority of what exactly ??

    Are you saying that you believe that over 50% of RV owners waste their money on a refrig fan that they don't need ??

    While I have no proof, I suspect it is WAY below 50% and those that don't are generally quite satisfied with how theirs works.

    Because in a small enclosed space like that it is absolutely a fact that you don't NEED a fan; convection currents handle the air distribution just fine in most cases.

    If you are talking about a minority of people responding to this and similar threads then yes, that's fairly obvious.
  • SCVJeff's avatar
    SCVJeff
    Explorer
    Jun 29, 2015
    Vulcan Rider wrote:
    SCVJeff wrote:
    If no fan were such a good idea then you wouldn't have them in residential fridg's, and they wouldn't be installed in the new Dometic's.


    Because they are designed to work properly WITH a fan.
    Those without them are not.

    Some will work with a fan and, as pointed out here, some will not.
    The fan is not "necessary" in either case.
    "Necessary" is a matter of opinion and you are far into the minority on this one. There is no possible way you can prove that a dead air ice box (and thats all it is at that point) works better than one capible of circulating air. Whether or not the OP's got his fan in the wrong place Is irrelevant to your comment.
  • Ed9824v's avatar
    Ed9824v
    Explorer
    Jun 29, 2015
    Vulcan Rider wrote:
    SCVJeff wrote:
    If no fan were such a good idea then you wouldn't have them in residential fridg's, and they wouldn't be installed in the new Dometic's.


    Because they are designed to work properly WITH a fan.
    Those without them are not.

    Some will work with a fan and, as pointed out here, some will not.
    The fan is not "necessary" in either case.


    I am a fan man, BUT in residential refrigerator the entire cooling system is in the freezer and then a set about of air is blown down with FAN to the refrigerator portion.

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