Dehumidifier not working

Discussion in 'The Projects Forum' started by Dalaran, Apr 27, 2011.

  1. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    I am having problems with my de-humidifier so I am trying to rule out a few components before blaming the compressor.

    There is a relay which takes the white wire from the wall socket and has 2 outputs connected to the compressor. The black wire from the main goes to the 3rd and final connection on the compressor.

    Where I am getting confused is this does not seem to be an ordinary relay. From the white wire connection to one of the outputs there is 0 resistance. On the other output however there is approximately 5ohms. Looking at the schematic it labels it relay but shows a resistive connection between the 2 outputs. I took a picture but it was basically worthless being from my phone. Is this normal? Why is there a few ohm difference between the outputs? Why does there need to be two outputs from the white wire both to the compressor?

    Thanks again!
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    Can you describe the problem?
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,118
    3,042
    Is it the humidistat? Most home dehumidifiers use a "plastic" strip that changes length at different moisture levels, thereby triggering the switch. These things are usually about 3" long and maybe 3/4" x 3/4". The user sets the humidity level by turning a shaft that comes out of this thing.
     
  4. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    The light and fan comes on but the compressor does not kick in. I will try to get a more detailed picture of the schematic, or put one together in multisim.

    I will check the humidistat... is this the most common cause of failure?

    Thanks.
     
  5. BillB3857

    Senior Member

    Feb 28, 2009
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    It sounds to me that you are looking at the starter relay. The main winding motor current goes through the coil of this relay and since a motor, when power is first applied, draws locked rotor current, the relay will pick up. When it picks up, it connects power to the start winding of the motor. As the motor comes up to speed, the current drops below a value that will maintain the relay in a picked up condition. The motor then continues to run on the main winding.
     
  6. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    Thanks for the reply. Could this maybe be the relay then that I was mentioning above? The connector for the white wire from the mains that attaches to this relay seemed to have a brown (maybe burnt) tinge to it. This is the one where I measure a short from the white wire in to 1 compressor output and about 5ohms to the other compressor output.

    Thanks again.
     
  7. BillB3857

    Senior Member

    Feb 28, 2009
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    Can you draw a diagram of what you have, or better yet, is there a diagram inside the cover?
    If my guess is right, it will look something like the attached, but with a humidistat in series with the line hot lead.
     
  8. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
    168
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    This is very similar to what I have. The input side of the relay to one output I meausure 0ohms, from the input to the other ouput of the relay I measure 5ohms. Does this seem correct? The input side of this relay is where I saw the brownish tinge to the connector.

    Thanks.
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    If they are 1/4" slide connectors, the discoloration may be due to a loose connection creating heat. Is the connector discolored, also?
     
  10. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    They are 1/4" slide connectors, the connector is slightly discoloured but more so the plastic surrounding it.

    Can someone explain to me the reason why the relay would be directly shorted from input to output #1 and have 5ohm resistance from input to output #2?

    Thanks!
     
  11. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    If the contacts are welded together, that would explain the 0 ohms. It should be open unless the motor is trying to start. The 5 ohm reading could be the coil, but seems high. Can you take the relay apart (remove the cover)?
     
  12. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    No, the relay won't come apart without doing some real damage.

    Sorry I haven't had a chance to put up the schematic yet... I had actually taken it over to my Dad's place to work on it there and did not bring it back home with me.

    Thanks again.
     
  13. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    Since it appears to be toasted anyway, try a good hard smack on the table in various orientations. Sometimes, a welded contact can be broken loose that way. If you then get infinite ohms and 5 ohms you will have confirmed a welded contact. If it was welded, your compressor is probably toasted as well since the start winding would have stayed energized continuously. They simply are not designed for that. It really sounds like it is time for a new de-humidifier.
     
  14. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
    168
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    Thanks again. Still no luck with the relay. After smashing it on the table a few times I still get the 0ohm and 5ohm readings.

    Is there a way for me to test this relay opening and closing by maybe hooking up a AC source to it? What measurement readings would I get in the two states?

    Cheers.
     
  15. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
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    This is probably the most important part of Bill's post. While all of this quote is important, the bold text is really good advice. Whether or not you get that relay working isn't relevant. If the contacts are welded it is highly unlikely that your compressor motor survived!
     
  16. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    One of the first tests of any relay is to check for proper contact operation. If a NO (Normally Open) contact is showing zero or very low ohm readings, the realy is BAD! NO further testing is necessary since it has already shown bad responses to the first test. Since it is obvious that you have no two terminals that are open with respect to each other, your relay is BAD! As I posted earlier, that failure mode will also destroy the compressor winding. Time to cut your losses (time spent) and replace the entire dehumidifier.
     
  17. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
    168
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    Completely understood. Didn't realize that one contact was to be NO while the other is NC. The schematic made it look as if there was suppose to be some resistance between the two output posts. Once again, thanks for all your help/time.
     
  18. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    If you look at the schematic I posted in Post #7, Terminal #1 ties to line, Terminal P ties to the RUN winding and Terminal A ties to the start winding. The sense coil ties between Terminal #1 and Terminal P and measures the starting current. When the start current is high, the plunger (the inverted T inside the coil) will pull the lower bar up to short between Terminal #1 and Terminal A. This supplies power to the start winding until the motor comes up to speed, at which time the current reduces to the point that a spring inside the relay opens the Terminal A to Terminal #1 contact. There is no Normally Closed contact on this type relay. There is only one Normally Open contact and a coil. The coil shares a terminal with the Normally Open circuit.
     
  19. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
    168
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    Well now I can say "completely understood".

    Thanks very much for your prompt and informative responses throughout.
     
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