LG refrigerator model LBN2251#** problems

[herman]

I hope that someone can either help me or perhaps refer me to a technical group such as this one specializing in refrigerators. This is a bottom freezer unit that we got four years
ago. The refrigerator section is running between 40 and about 46 degrees and the freezer is at 42.

We cleaned all the dust out of the back and bottom and there doesn't seem to be any improvement. I am an electronics technician however I don't know too much about refrigerators except that they are expensive to have fixed. I was hoping that someone might be able to point me in the right direction to troubleshoot this thing.

I did find something online that mentioned checking the defrost heater in the freezer
section. The heater looked good. It then mentioned to check the fuse that is wire tied to the defrost coil for continuity. Well there appears to be two fuses, or perhaps they are sensors? One is connected on a pair of orange wires and the other connected with a brown and red. The orange pair shows continuity but the other pair is open. Of course one device may be a thermistor too or it could be a NO while the other could be NC. My real problem is that I really don't understand enough about the theory of operation. The unit is
only four years old.

I now have a service manual that someone sent me but it is not very well written and a bit confusing.  We're going to try to run through some of the diagnostics tomorrow. I should mention that there was a slight amount of ice on the freezer coil only in the area of
what looks like those two thermal devices. I don't think  that the ice was enough
to cause any problems. As soon as we pulled power to check this four wire device the small amount of ice quickly melted.  This  one device is a bit ambiguous though. They don't really spell out exactly what it is. It is wire tied to the upper right side of the freezer coil and looks like a sort wafer with four wires on it. It appears to be two separate devices. and as I mentioned, one appears to have continuity and the other seems be open.  If in
fact they are two fuses then maybe we found the problem, (or the result of it). I can't tell from the schematic why there are two devices fastened to that freezer coil and exactly what they are. It is for certain though, they are in intimate thermal contact with
the coil. I was wondering if anyone is familiar with this model and perhaps you know how to help me. Thanks for any assistance, Lenny

Model LBN2251

[tgoods]

The two orange wires are the defrost thermistor.  The red and brown wires are the thermal fuse.  You get both in the sensor assembly part number 6615JB2005C. Since the fuse is open it is definitely bad.  

With a defrost problem you should see the evaporator completely plugged with frost.  If you only see a little bit of ice or frost, you probably have a sealed system problem too.  I believe LG has a seven year warranty on the sealed system.  If so, you should call LG to repair it for free because sealed system repairs are expensive.

[herman]

Well that really clears up a bit of uncertainty. So I'm assuming that this is a 72 degree C thermal fuse on the brown and red I noticed on the schematic? Now if the fuse to the defrost coil is open then does that mean that there was a problem with the defrost duty cycle? Will this fuse open on over current as well as over temperature? If it will then how would we know which condition caused it to open? And if I could just ask one more question, does approximately 0 ohms at ambient room temperature seem correct for the thermistor? This seems pretty low to me. Thank you so much for helping me with this. You may be saving my marriage. Lenny

[tgoods]

Your thermistor is shorted which probably caused the over heating that blew the fuse. Good thing one part replaces both, huh?

[herman]

I'm going to order the part on Monday. Thanks for all the help. I'll let you know how we make out. Lenny

[herman]

I haven't ordered the part yet because of something you said about the sealed system.  I checked and the defrost fan is running. In fact there seems to be a fan running all the time. The fan seems to stop when I open the refrigerator door. I can't really tell what this fan is  though.

We have definitely determined that the four terminal device that is wire tied to the defrost coil is bad. The fuse section is open and the thermistor reads 0 ohms. As you suggested the fuse probably opened because the thermistor shorted. Makes perfect sense.. But what you said about the ice build up that I should expect to see on the coil (that I'm not seeing), makes a lot of sense too.

I'm sure that this thermistor/ fuse part is bad but then why did it go bad.?  If as you suggested the sealed system could be at fault then could that have damaged this part? (LG calls it a defrost control). I just don't want to call a repairman if the sealed system is not the problem. Money is really tight right now and if this simple electrical problem would fix the box then that would really help us out.

In theory can you venture a guess as to what kind of performance I could expect out of this unit with the thermistor/ fuse bad? In essence what I am asking is in theory now If the thermistor is shorted and the fuse is open, as they now appear to be for whatever reason, under otherwise normal conditions will that scenario affect refrigerator cooling and the freezer freezing? Or will it as you said just cause the freezer coil to ice up after awhile as they did in the old refrigerators?. If that's the case then replacing this part may fix the defrost problem/ cycle  but will it affect cooling? From what I'm understanding it doesn't seem like it would have anything to do with cooling. So just replacing this part will not get my freezer to work it seems. Is there a foolproof method to absolutely rule out/ rule in the fault? Thanks very much for helping me with this, Lenny

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[tgoods]

Put it back together and see if will cool down.  It takes a good week or more for the frost to build up to a point that it will stop cooling.  If it doesn't cool, you know there's something else wrong.