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  1. #1
    kln's Avatar
    kln Guest

    No Power for Defrost Timer Motor



    My frost-free 2 door (top-freezer) 280 Litres refrigerator is only 4 months old and stopped working altogether on Christmas eve. When called for service under the warranty, the defrost timer was reported faulty and replaced. But my fridge kept running non-stop all the time. When I again called the service personnel, they reported that it is "normal behaviour" as long as there was proper cooling (which is the case). But got concered as my energy meter was galloping and as my fridge was not behaving like this before. The thermostat (inside the freezer compartment) is set to 3 on a scale of 9 and the rotaty switch in the lower compartment (I think it regulates the air supply) is set to "Normal". When I rotate the thermostat to lower setting (2 on a scale of 9) after it has been running for a while, I can hear the compressor stop. But again it keeps on running without any halt. Could this be a faulty thermostat? To my surprise, even though it is running all the time, there is no "over cooling" of foods (the cooling effect seems to be the same as before).

    The fridge never kicked into the defrost cycle at all. When I manually turned the defrost timer to the defrost cycle, it would never kick back to the run cycle. So I doubted if the defrost timer is getting power to run its motor at all.

    I called the service personnel again and they have once again replaced the defrost timer (when I wasnt at home). And the same behaviour continued. So, I sat down to understand the circuit diagram on the back plate and found that power was routed thru the "defrost heater" and then a "thermal fuse" to the defrost timer motor. With a line tester, I figured that the defrost timer motor did not get any power at all (no matter which cycle I manually kicked it in). Could this be because of blown thermal fuse? I also noticed a "bi-metal" switch in the circuit diagram (defrost thermostat I think). Could this be because of a faulty bi-metal switch. Or is it a combination. i.e a faulty bi-metal switch has allowed the defrost heater to over heat and blown off the fuse?

    I dont want to open up the fridge as it is still under warranty. But atleast I want to ensure that the service personnel I have to call again are doing the right thing to fix the problem. I dont want to have the "defrost timer" changed for the third time without any reason.

    Any thoughts on this are welcome.



  2. #2
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    Re: No Power for Defrost Timer Motor

    When defrost is triggered, usually the timer motor loses all power, and electricity instead goes through the thermal fuse and coil heater which heats up the evap to defrost.
    Once a programmed termination temperature is met, a themally operated switch* opens, giving power back to the timer motor and in about 10-30min drip time the defrost timer will click over and the compressor will start cooling again.
    So if you have a simple mechanical based fridge, you need to check the thermostat, thermal fuse, coil heater, *klixon (thermally operated switch) and defrost timer.

  3. #3
    kln's Avatar
    kln Guest

    Re: No Power for Defrost Timer Motor

    Yes, the defrost timer is a mechanical one (I am assuming that it what you are asking when you say "Simple mechanical fridge"). But even in the run cycle (when I have manually put the defrost timer to it), there is no power to the defrost motor. All the more, when I have manuall put the defrost timer to defrost cycle, there is no water collection in the water tray behind the fridge. It just stays put and never reverts to the "run cycle".

  4. #4
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    Re: No Power for Defrost Timer Motor

    Quote Originally Posted by kln View Post
    Yes, the defrost timer is a mechanical one (I am assuming that it what you are asking when you say "Simple mechanical fridge"). But even in the run cycle (when I have manually put the defrost timer to it), there is no power to the defrost motor. All the more, when I have manuall put the defrost timer to defrost cycle, there is no water collection in the water tray behind the fridge. It just stays put and never reverts to the "run cycle".
    Could you somehow make photo of that schematic diagram and post here, or somewhere else and provide us with link to that picture?

  5. #5
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    Re: No Power for Defrost Timer Motor

    The timer sounds like it is wired wrongly.

    Give us the make and model of the timer unit.

    Chillin
    IF AT FIRST YOU DON`T SUCCEED.
    DESTROY ALL EVIDENCE THAT YOU TRIED!
    and go get a cuppa

  6. #6
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    Re: No Power for Defrost Timer Motor

    Quote Originally Posted by kln View Post
    All the more, when I have manuall put the defrost timer to defrost cycle, there is no water collection in the water tray behind the fridge. It just stays put and never reverts to the "run cycle".
    So you need to check continuity of the thermal fuse, heater element and klixon like I explained the circuit before

  7. #7
    kln's Avatar
    kln Guest

    Re: No Power for Defrost Timer Motor

    Hi all,
    Thanks for the tip. Since the fridge is on warranty, I called up the service personnel and reported my findings (about lack of power at the timer motor etc.). The defrost bimetal switch was found faulty and replaced. And the problem stands solved. However, I shall post the circuit diagram shortly and would like to know how it was not the thermal fuse and the bimetal switch instead that was faulty.

    Another question. When I turn (mechanical) the thermostat in the freezer compartment to a higher temperature (less chiller) when the compressor is running, it doesnt stop it immediately. However, when I turn it to a lower temperature (chiller) when the compressor has stopped, it starts running. Is this normal behaviour? I just want to make sure that there is nothing wrong with the thermostat. Anyway, it does perform all the intermitent starts and stops when the fridge is running. I just want to make sure that the extent of cooling that can be adjusted thru the thermostat is remaining functional. Any thoughts on this are most welcome.

    Regards
    KLN

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