Help with dehumidifier repair. Is this a thermistor??

Discussion in 'Technical Repair' started by Terry annis, Jan 7, 2019.

  1. Terry annis

    Thread Starter New Member

    Jan 7, 2019
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    hi all, i have a EcoAir DD1 CLASSIC MK5 Desiccant Dehumidifier that after a few minutes goes in a check mode then turns off. if i unplug it and then plug it back in it does the same thing.

    i have narrowed it down to what i think is a thermistor.

    there are two components that are screwed to the heating element casing



    [​IMG]




    [​IMG]


    I think the larger one is a thermal switch and the smaller one is a thermistor??

    if i unscrew the two components from the heating element casing the machine works fine and doesn’t cut out.

    if i leave the thermal switch attached to the element and move the thermistor away the machine works fine and doesn’t cut out.

    if i leave the thermistor attached the the element and move the thermal switch away the machine cuts out after a few minutes.

    i think i will try and replace both components, i have found the thermal switch but there isn’t any numbers or codes on the thermistor , does anybody know which thermistor i would need to buy? if it even is a thermistor?

    i dont believe the heating element is a fault as i think it would ether work or not work if it was faulty, am i correct in thinking that?

    Also could anyone explain why the machine would cut out if it is a faulty thermistor that is the problem.

    thank-you for and advice in advance



    [​IMG]
     
  2. drc_567

    AAC Fanatic!

    Dec 29, 2008
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    ... cannot be positive, but the plastic encased part may be a thermal fuse. As the heating element reaches a certain temperature, the fuse will open and stop the temperature rise. ... They are subject to failure after so many operating hours.
    If it is a thermal fuse, it will likely have a temperature marking ... so many degrees ... printed on it so that it can be replaced ... If you can safely access it, test the room temperature continuity. ... always with the device unplugged.
     
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  3. Terry annis

    Thread Starter New Member

    Jan 7, 2019
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    Hi, thank you for the swift reply. I believe the larger one is a thermal fuse yes (sorry I described it as a thermal switch) this fuse seems to be working ok as the machine doesn’t switch off when only that is in place on the element casing.
    It’s really the other part that is confusing me as it has no markings or numbers on it.
     
  4. jpanhalt

    Expert

    Jan 18, 2008
    6,564
    1,303
    Hi Terry,

    I can't make out the unknown device clearly enough to be sure. If it looks like this:
    upload_2019-1-7_9-6-37.png

    it is likely a thermister. They are common in temperature control devices. I was puzzled by one in a battery pack (see here: https://forum.allaboutcircuits.com/threads/craftsman-nicd-battery-packs.155195/ ). It had a cold resistance of 10k to 13k ohm and when heated the resistance dropped. Hence a simple current monitor could tell the device's temperature.

    Does the refrigerator function cool? I would be worried about bypassing those safety devices, if the refrigerant was not cooling (e.g., too low).
     
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  5. Terry annis

    Thread Starter New Member

    Jan 7, 2019
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    Ah yes it looks exactly like that. Thankyou!!
    That would make sense that a current monitor is thinking the device is overheating and shutting it off.
    Hopefully it’s not actually overheating and it’s just the faulty thermistor.

    The dehumidifier is a desiccant version so it blows hot air onto a honeycomb wheel type thing, not refregerent type.

    It runs normal temp when it does run.

    How would one test the ohms value so a replacement can be found? Or is it likely to be a certain value or certain type?
     
  6. LesJones

    Well-Known Member

    Jan 8, 2017
    1,797
    478
    This will not help with the solution to the problem but it may help others jumping to the wrong conclusion about a "Desicant dehumidifier". I had wrongly assumed it was the type which had to have the desicant material replaced when it had absorbed the moisture in the air. Here is a link which describes how the TS's dehumidifier works.

    Les.
     
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  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
    5,922
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    Les, you beat me to it. If this is being used where the humidity is already low, the unit is probably working correctly. In the link if you look at "note 2" about a third of the way down the page, that may be what is happening.
     
    jpanhalt likes this.
  8. Raymond Genovese

    Well-Known Member

    Mar 5, 2016
    1,098
    635
    If you look in the PDF manual under troubleshooting, you will see the conditions under which the behavior that the OP describes occurs. This includes the low humidity condition already mentioned. It also mentions clogs.

    Seems like a replacement of an unknown component that *may* be a thermistor is ill-advised without more information. The safety features that prevent over heating/use appear to be working.

    Have you looked at other possibilities?
     
  9. Terry annis

    Thread Starter New Member

    Jan 7, 2019
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    the light that comes on is a fault light so I don’t believe it has to do with low humidity. When it’s working correctly the machine always runs what ever the humidity, it’s only the heating element that turns off and on according to the humidity.
     
  10. Terry annis

    Thread Starter New Member

    Jan 7, 2019
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    I’m pretty sure it is a thermistor, I thought replaceing that cheap component would be the easiest way to check if it was actually over heating or it is actually a faulty thermistor.

    Maybe you are correct and the safety features are working as the should but I’ve thoroughly cleaned the machine and filters so iv rulled out that being the cause of over heating, the thermal fuse doesn’t cut the machine out when only that component is attached to the element housing, this is why I’m questioning if the machine is really over heating, because is it was surely the thermal fuse would blow as it’s the second safety feature after the thermistor?

    Can a heating element go faulty and over heat?
     
  11. jpanhalt

    Expert

    Jan 18, 2008
    6,564
    1,303
    I learned something about desiccant dehumidifiers today. Interesting approach. Makes me wonder what the desiccant and exhaust temperature are, and/or how the exhaust is cooled cooled down so as not to cook passersby.

    As an aside, a few years ago, I got a "drainless" room A/C that worked by passing the warmed air over the condensed water to re-evaporate it in the exhaust. That worked on moderate days with low humidity. On a hot day with high humidity, the heated exhaust was not up to the task, and the device overflowed. As one might expect, there were conspicuous warnings about the hot exhaust, which was never even near 60°C (tested by hand). Fortunately, there was still a drain connection on the device.

    Back on subject, that "uncertain" device can be tested easily by disconnecting one end. Attach an ohmmeter to it and warm with a hairdryer. The resistance should markedly increase or decrease (the latter is probably more likely). The one in my battery pack started at approximately 10K and decreased a lot with just warm air.
     
  12. LesJones

    Well-Known Member

    Jan 8, 2017
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    Hi Terry,
    Have you tried contacting the manufacturer of the device to buy the spare parts from them ? That way you should get the correct themistor.

    Les.
     
  13. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    It could also be the 'humidistat'.
     
  14. Terry annis

    Thread Starter New Member

    Jan 7, 2019
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    its defiantly something to do with the thermistor as the unit works fine when the thermistor is unscrewed and moved away from the heating element casing.
     
  15. Terry annis

    Thread Starter New Member

    Jan 7, 2019
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    i have tried but they don't want to know :(
     
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