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Forum Index => Range, Oven & Cooktop Repair => Topic started by: longbid on May 29, 2012, 01:55:06 PM

Title: LRFC25750 icing up
Post by: longbid on May 29, 2012, 01:55:06 PM
New member with a question on an LG LRFC25750 refrigerator.
The unit every 4 -6 hours starts the motor in the bottom unit and it sounds like the blades are hitting ice.
The ice drawer and and right side drawer had a build-up of frost.
One of my tech buddies said it might be the 24 hour timer as being bad,
Does anyone have an idea or a service manual?
Thanks for the input.
Nice site. O0
Title: Re: LRFC25750 icing up
Post by: AJ on May 29, 2012, 02:10:46 PM
Hi

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

Quote
The unit every 4 -6 hours starts the motor in the bottom unit and it sounds like the blades are hitting ice.
Have you taken it apart and looked at the fan to see if that is the case?



Title: Re: LRFC25750 icing up
Post by: clman on May 29, 2012, 03:00:02 PM
All LG ref are adaptive defrost type units. A thermistor monitors the evaporator tubing temp and sends the info to the m.PCB which puts the unit into defrost. Therefore it defrosts when it needs to rather at a definite predetermined time interval. That being said if the noise stops when you open the freezer door / drawer and starts when you close the door it going to be either the evaporator fan blade hitting frost / ice build up around the shroud or bad motor bearings. Unplug the unit and poem the freezer for about three hours. Then plug it back in and if the noise does not return in a couple of days change thedefrost controller. If the fan bearings are bad the occurance of the noise will not be consistant and will likely reappear within the same time frame it has been occurring in already. A teardown of the freezer panel will show you if frost build up is occurring around the shroud.
Title: Re: LRFC25750 icing up
Post by: longbid on May 29, 2012, 03:13:57 PM
When I open the refrigerator doors the noise stops.
Opening the freezer door and the noise contiues.
I have used a heat gun to speed up the icing by the motor and it goes away for a few months then comes back.
Where is the defrost controller?
Does that still sound like the problem?
Thanks for all your inputs.
Mike ::)
Title: Re: LRFC25750 icing up
Post by: AJ on May 29, 2012, 05:25:35 PM
Quote
Where is the defrost controller?

On the back of the refrigerator.
LG Refrigerator Main Control Board Part # 6871JB1284L (http://www.repairclinic.com/PartDetail/Main-Control-Board/6871JB1284M/1266871?replacedManufacturerPartNumber=6871JB1284L)

(http://www.RCappliancepartsimages.com/dbImages/i/00002315/Main-Control-Board-6871JB1284M--00697064.jpg) (http://www.repairclinic.com/PartDetail/Main-Control-Board/6871JB1284M/1266871?replacedManufacturerPartNumber=6871JB1284L)
Title: Re: LRFC25750 icing up
Post by: clman on May 29, 2012, 06:10:26 PM
It's definitely a defrost controller issue. It's located behind the evaporator panel strapped to the evaporator coil. I'm sure the forum parts link will enable you to see what it looks like.
Title: Re: LRFC25750 icing up
Post by: AJ on May 29, 2012, 06:11:57 PM
It's definitely a defrost controller issue. It's located behind the evaporator panel strapped to the evaporator coil. I'm sure the forum parts link will enable you to see what it looks like.

Your talking about a electronic control board?

Title: Re: LRFC25750 icing up
Post by: longbid on May 29, 2012, 08:32:39 PM
You guys are great,
Any way to test the board to know for sure?
Volt ohms etc.?
Any capacitor or resistor that is common fault?
Is the defrost controller  part of the main board or separate?
Thanks again,
Mike :D
Title: Re: LRFC25750 icing up
Post by: clman on May 29, 2012, 09:31:32 PM
No. I'm talking about the adaptive defrost controller inside the freezer attached to the evaporator coil. Location # 400A on the exploded view. Part number: 6615JB2005H.
Title: Re: LRFC25750 icing up
Post by: AJ on May 29, 2012, 09:37:37 PM

Does not look like a adaptive defrost controller to me.
LG Refrigerator Defrost Sensor Part # 6615JB2005H
Title: Re: LRFC25750 icing up
Post by: AJ on May 29, 2012, 09:42:49 PM
Maybe we are talking about the same thing, not sure.
Title: Re: LRFC25750 icing up
Post by: clman 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.
Title: Re: LRFC25750 icing up
Post by: AJ on May 29, 2012, 09:56:01 PM
 O0
Title: Re: LRFC25750 icing up
Post by: clman on May 29, 2012, 10:04:13 PM
You may want to re-read my previous post. I have added more info.
Title: Re: LRFC25750 icing up
Post by: AJ on May 29, 2012, 10:07:51 PM
Ok, very good to know, thanks.
Title: Re: LRFC25750 icing up
Post by: longbid 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
Title: Re: LRFC25750 icing up
Post by: AJ 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 (http://appliancejunk.com/forums/index.php?action=store;sa=view;id=115)



Title: Re: LRFC25750 icing up
Post by: clman 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.
Title: Re: LRFC25750 icing up
Post by: longbid 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
Title: Re: LRFC25750 icing up
Post by: clman 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.