Norcold Heater

Discussion in 'Talkback' started by cjcj, Jul 30, 2008.

  1. cjcj

    cjcj New Member

    How long should I expect the Norcold AC Heater (part # 621702) to take to start cooling the refrig? I feel the 3/4" line getting warm / hot - but it seems to take 20 minutes or so before the tube is all warm / mildly hot.

    Is the heater tube on it's way out and needs to be replaced?

    Thanks
     
  2. C Nash

    C Nash Senior Member

    Re: Norcold Heater

    Welcome to the forum. Do you mean how long before the fridge starts cooling?
     
  3. cjcj

    cjcj New Member

    Re: Norcold Heater

    Yes - how long

    Thanks
     
  4. elkhartjim

    elkhartjim Senior Member

    Re: Norcold Heater

    It starts cooling quickly but it will take up to 24 hours or longer to lower temp to 35-40 degrees.
     
  5. C Nash

    C Nash Senior Member

    Re: Norcold Heater

    You should start feeling some cooling in the freezer box after 30 mins or so depending on how hot it was to start with. Like Jim said it will take around 24 hrs to get to the lower temps. Best to chill everything before puting them in the box if possible.
     
  6. cjcj

    cjcj New Member

    Re: Norcold Heater

    Great! Thanks. It took about 20 to 30 minutes and you could tell the freezer was starting to cool. Just cursious - why the freezer first - then the fridge? I found a Norcold Repair manual that seems to show resistence measurememts for the heater (200W = 61OHMS - +/- 5%). I'll let it run overnight and see how it goes.

    Great forum - and thanks again. I'm sure I'll be back with more questions or replies!

    Thanks again!
     
  7. scarince

    scarince New Member

    Re: Norcold Heater

    Freezer first because the cooling solution is pumped to top of the unit, then it travels down back to the boiler as it cools. From the top down it passes through the freezer evaporator first, then on down to the fresh food compartment, so you see the cooling on top first.
     
  8. Kirk

    Kirk Senior Member

    Re: Norcold Heater

    The cooling process in an RV refrigerator works by absorption, and the coolant moves by convection flow and has no moving parts, pumps, or compressors.

    What happens is that a mixture of ammonia & distilled water is heated in a boiler and it turns to a vapor. That vapor will rise to the very top of the refrigerator because hot vapor rises and cooler liquids flow down. The heater vapors are under pressure due to the absorbed heat. When it reaches the top of the refrigerator, it enters the cooling coils of the freezer first, and as the pressure is released the vapor expands and it also absorbs heat energy from the coils, thus lowering the temperature inside of the freezer compartment. The expanding vapor then flows down through the coils and enters the coils of the chill box part of the refrigerator. Any remaining vapor pressure then fully expands again absorbing more heat energy from the chill box as it slowly moves toward the heat exchanger.

    In the heat exchanger, air moving upward through the back of the refrigerator cools the now low pressure vapor back into a liquid and it flows on down, into the liquid reservoir at the bottom of the refrigerator. From that reservoir the liquid runs into a boiler where either a propane flame or an electric heater supplies the heat to vaporize the mixture again and the pressurized vapor again rises to the top, due to convection because hot always rises. Since the most vapor reaches the freezer first, it also will cool first and if there isn't enough cooling, or if the freezer is too warm, all vapor pressure will be released in the freezer and so no effect is seen in the chill box until the freezer is fairly cool and no longer supplies enough energy to allow the vapor to completely expand.

    The RV refrigerator is designed in that way for two reasons. First, it means that when cooling ability is limited, the frozen items will be protected most. Second, it also makes for much more simple controls since the designer just puts a thermistor on the cooling coils of the chill box which is then used to control the cooling operation. With this design, by using the proper ratio of cooling coil size the freezer will stay a proper temperature differential below that of the chill box and so one control does the job.

    This is a pretty simplified explanation of how they work, but it should give you some idea of how you can use heat, to cool a refrigerator and even to freeze things. The key is that when a pressurized gas is allowed to expand it has to absorb heat energy, no matter what the surrounding temperatures may be. The heat that is removed in the expansion process is then removed from the refrigerator cooling unit in the coils at the very back of the flue area by the air that rises through the cooling unit and out the top vent. That is also the reason that the addition of a small fan to the rear of the refrigerator in hot weather can improve the cooling of the refrigerator, since excess heat has to be moved out the top of the refrigerator.
     
  9. elkhartjim

    elkhartjim Senior Member

    Re: Norcold Heater

    Now, all we gotta do is get Tex to explain why ice cream stays soft in the freezer and the story will be complete.
     
  10. Guest

    Guest Guest

    Re: Norcold Heater

    oh no not agian ,, jim the ice cream thingy :eek: :eek: :eek: :eek: ;) :laugh: :laugh: :laugh:
     
  11. C Nash

    C Nash Senior Member

    Re: Norcold Heater

    Cause it aint frooooze Jim but I bet Tex will give a Dr Tex answer ;)
     

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