Panasonic Inverter Refrigirator

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Panasonic Inverter Refrigirator

Unread post #1 by joey81 » Mon Mar 10, 2014 3:37 pm

I have a Panasonic inverter refrigerator, in service for more than four years now. The freezer is at the bottom, vegetable compartment in the middle, and the ref compartment on top. The evaporator coils is on the bottom, behind the freezer compartment (FC). The upper compartments are cooled by circulating cold air.

About a month ago we noticed the upper compartment isn't as cold as it used to be. And it got worse a few days later. FIrst I thought it was the fan, but I can hear it running when I close the door, and it stops when I open the door. Later we discovered that when we unplug the ref from the mains for 12 hours and plug it again, the upper compartment gets cold again. And the problem returns after a couple of days.

By then I already purchased the repair manual somewhere online (pdf copy). It and other members of cab1net, helped me conclude that the defrost heater is somehow not firing and the buildup of ice in the evaporator eventually blocks the path of circulating air.

Last week I called a local repair shop and they sent a technician over. Watching them taught me how to open up the unit (I couldn't figure out how to remove the clear plastic shelf, and I fear I might break it). They connected the heater to 220V and it works. They said it might be the thermal fuse or the defrost sensor. The parts aren't readily available and has to be ordered by their shop.

They assembled the unit back together and I paid the "diagnosis fee" of P200, plus tip. I figured while waiting for the parts to be available I can manually defrost the evaporator coils by directly connecting the heater to 220V. So I removed the panel at the back to expose the mother board. I removed the connector to for the heater and measured the resistance across the 2 wires: 266 Ohms. Close enough to the 265 specified in the repair manual. That also means the thermal fuse is still working.

After four days, the upper compartment started to "heat up". So I connected the heater (via the connector at the back) to 220V, and watched the meltwater dripping to the defrost pan pan. Left it like this overnight.

The following morning I unplugged the heater and plugged the ref... It worked!

This afternoon I decided to document what I did. I wanted to take a picture of the multimeter reading 266 Ohms. Nothing... the circuit is open! I somehow blew the thermal fuse!

I went back to read the repair manual. Only now I discovered that the micro-controller limits defrosting time to 60 minutes max. And that the thermal fuse blows at 72C. So leaving the heater plugged overnight was not a good ideal. Also I want to bang my head against the wall because this morning I went to Deeco in Quiapo to buy thermal fuse for my electric fan!

Now that I'm reading the repair manual, I came across this:
Defrosting: Full-automatic control Start : micro-computer ; Finish : Defrost sensor

The facts:
- heater is intact
- thermal fuse (in series with heater) is intact (before I screwed it)
- defrost sensor is for stopping the defrost cycle

What could be the reason why its not defrosting?

Software doesn't degrade over time.

If the microcontroller is busted, why only the defrost function is affected? All other functions seem OK.

Power to the heater is gated via a relay (http://www.omron.com/ecb/products/pdf/en-g5nb.pdf). As of the moment that is the only thing I can think of.
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Re: Panasonic Inverter Refrigirator

Unread post #2 by joey81 » Mon Mar 10, 2014 3:48 pm

Here's what I'm going to do now: solder wires to the coil terminals of the relay. So I can easily probe it.

Then let the fridge operate normally. After some time the defrost cycle will be triggered. This should be reflected on the voltage across the coil terminals of the relay. The defrost sensor (a thermistor actually) is supposed to trigger the controller to stop the defrost cycle at 11 degrees C. Since the heater is out of commission, the relay should stay ON.
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Re: Panasonic Inverter Refrigirator

Unread post #3 by adzz » Mon Mar 10, 2014 4:08 pm

Sir Joey ,

Is your Ref model by any chance NR - BW465VNPH?

Ours is this model , if so then I have to subscribe to this .


Btw thanx for the shipment , I'll just wait for it to arrive :angel:
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Re: Panasonic Inverter Refrigirator

Unread post #4 by joey81 » Mon Mar 10, 2014 4:21 pm

NR-D512X.

Although its different model to yours, the control principles should be the same or similar.
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Re: Panasonic Inverter Refrigirator

Unread post #5 by bejiboys » Mon Mar 10, 2014 6:47 pm

Wild guess: Maybe the thermistor is defective (high resistance) and the uC is not entering the defrost cycle because it requires sensing a resistance equivalent reading around the normal temperature inside the ref. It does not seem to make sense to turn on the heater to defrost if the measured temperature is already => 11degC.

Make sure you have something to record or latch the DMM measurements in the 2nd post. You wouldn't want to wait for long just to check if the defrost cycle actually happens. :) Discard the guess above if your results show the heater is triggered.

Good luck, Dennis. :)
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Re: Panasonic Inverter Refrigirator

Unread post #6 by joey81 » Mon Mar 10, 2014 7:11 pm

bejiboys wrote:Wild guess: Maybe the thermistor is defective (high resistance) and the uC is not entering the defrost cycle because it requires sensing a resistance equivalent reading around the normal temperature inside the ref. It does not seem to make sense to turn on the heater to defrost if the measured temperature is already => 11degC.

Make sure you have something to record or latch the DMM measurements in the 2nd post. You wouldn't want to wait for long just to check if the defrost cycle actually happens. :) Discard the guess above if your results show the heater is triggered.

Good luck, Dennis. :)



Pwede.

"Cumulating the compressor running time of certain period or time after defrosting according to AT temperature"

This says temperature is also a factor in entering the defrost cycle. I just don't fully understand it means. :lolno:

Spray-an ko 'to ng Baygon pag hindi gumana. ;)
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Re: Panasonic Inverter Refrigirator

Unread post #7 by joey81 » Mon Mar 10, 2014 7:28 pm

The Omron relay
Image

Probe wires soldered
Image

Installed:
Image

Now we wait.
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Re: Panasonic Inverter Refrigirator

Unread post #8 by Ronnel » Mon Mar 10, 2014 7:35 pm

gezzzzz high tech pala ref mo may electronic board kaya pala madali masira my ref is almost 13yrs na still work pa rin :crazy:
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Re: Panasonic Inverter Refrigirator

Unread post #9 by bigfoot » Mon Mar 10, 2014 7:41 pm

You mean the heater doesn't work anymore even if connected directly to AC?

To help you in monitoring, attach a door chime/buzzer to the relay. :wtf:
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Re: Panasonic Inverter Refrigirator

Unread post #10 by joey81 » Mon Mar 10, 2014 7:46 pm

bigfoot wrote:You mean the heater doesn't work anymore even if connected directly to AC?


Yes. But probably just the thermal fuse. I left it plugged overnight kasi. :wtf:
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