Author Topic: LRFC25750 icing up  (Read 3067 times)

Offline AJ

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Re: LRFC25750 icing up
« Reply #10 on: May 29, 2012, 09:42:49 PM »
Maybe we are talking about the same thing, not sure.
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Offline clman

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Re: LRFC25750 icing up
« Reply #11 on: May 29, 2012, 09:52:50 PM »
Trust me it is. The term "adaptive defrost controller" when referring to this single part may be misleading. The m.pcb and this controller together make it an adaptive defrost control system. This is a thermistor and the high temperature limit for the heater. It is not the freezer room temperature sensor. It is only the evaporator coil temperature sensor for telling the m.pcb when to go into defrost and for how long. The controller thermistor is reading wrong and allowing the unit to come back on in cooling mode too soon. It starts cooling while there is still steam floating around behind the panel and inside the freezer cabinet from the heating / defrosting function. This causes frost build up in various locations. IE the frost build up around the shroud.

Also; although it is not the culprit in this particular event, overall frost buildup issues were addressed by changing the m.pcb software which changed the m.pcb part number to: 6871JB1284M for any units mfg prior to ser# 606KR**00001 ( 6/2006 ). It lengthened the time at which the cooling mode would be re-entered.

Typically if there was no frost issue till recently you m.pcb will not need to be changed.
« Last Edit: May 29, 2012, 10:03:29 PM by clman »

Offline AJ

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Re: LRFC25750 icing up
« Reply #12 on: May 29, 2012, 09:56:01 PM »
 O0
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Offline clman

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Re: LRFC25750 icing up
« Reply #13 on: May 29, 2012, 10:04:13 PM »
You may want to re-read my previous post. I have added more info.

Offline AJ

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Re: LRFC25750 icing up
« Reply #14 on: May 29, 2012, 10:07:51 PM »
Ok, very good to know, thanks.
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Offline longbid

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Re: LRFC25750 icing up
« Reply #15 on: May 30, 2012, 09:30:14 AM »
Thanks again AJ and clman for the clarification
Is there a test for the defrost controller?
And if so is it easy to get to?
Mike O0

Offline AJ

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Re: LRFC25750 icing up
« Reply #16 on: May 30, 2012, 09:39:41 AM »
More details can be found in the service manual, but I have attached a few pages of it here.
Maybe you will find them helpful.

The full service manual can be found here.
http://appliancejunk.com/forums/index.php?action=store;sa=view;id=115



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Offline clman

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Re: LRFC25750 icing up
« Reply #17 on: May 30, 2012, 01:16:24 PM »
Testing a thermistor is not easy to do accurately. You have to be sure your meter and thermometer are very accurate. Because the thermistor is incapsulated in clear plastic it will not make direct contact with what ever you use to bring it to a particular tempature. Temperature changes inside the assmy take longer than usual. Reference the chart in the serice manual for testing the sensor / thermistor resistance at a given tempature.

Offline longbid

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Re: LRFC25750 icing up
« Reply #18 on: May 30, 2012, 02:52:40 PM »
clman,
How does one reprogram the pcb?
Do I need to purchase a new board or can a service tech or DIY do t?
You and AJ have been an invaluable source and are much appreciated.
If I can ever help you out (I was a Canon printer rep and an automotive service consultant),please let me know!!
I also have the curent Mitchell and Alldata programs.
Thanks again for your answer to the above question!
Mike :D

Offline clman

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Re: LRFC25750 icing up
« Reply #19 on: May 30, 2012, 03:14:03 PM »
You don't ( and cant ) reprogram the m.pcb. That was a factory change that created a new part number for the m.pcb. The only way to get the new software is to change the m.pcb with the new part number one. And that's if your doesnt already have the newer type m.pcb.

You seem to be focused on the board and putting the cart before horse. As I said before, if you have not had frost issues in the freezer cabinet until just recently the m.pcb should be fine.

The bottom line is that you need either test the controller, as I described, or just change it. Then take it from there.