Defroster in the refrigerator

The timer controls heating elements placed strategically amongst the evaporator. It also shuts the compressor off and keeps it off until the defrost cycle has run its course. It is possible that the defrost timer cycle has lengthened due to a partial failure but it is only remotely possible as the usual failure is it fails to defrost. I have seen the contacts points of a defrost timer weld together however that results in the refrigerator not working at all. It is also possible for one of the heating elements failing resulting in a partial defrost that would lead to your unit not freezing and cooling properly. Your thermostat has nothing to do with defrosting unless it is part of some elaborate electronic controlled system found in a lavishly expensive refrigerator of which I have never encountered and of which I only mentioned as a remote possibility.

Why not run the defrost cycle manually for a couple of days and see how it works. Usually it takes about 2 hours max for the defrost cycle, My money is on the timer, there is not a defrost thermostat in most units I have ever looked at. Is there a schematic on the back or inside back of the unit? Try contacting the manufacturer for the schematic.

The defrost thermostat is buried with the heater and coils. It's not separate, if that's what you mean. There really should be one so that it stops heating once all the ice has melted and the temperature goes above 32C.

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Hi The timer seems to othewise work. It will restart the compressor when it finishes the cycle. It is possible that it is staying on too long but I'm tending to think it is the defrost thremostat. The unit is a newer GE model and doesn't have the wiring diagram but GE has a PDF breakdown of the parts on their web page. They show an electrical thermostat as Sam mentions on the top of the evaporator coils. The air from the back is definitely hotter than freezing temperatures and it might make sense that the thermostat was not opening. It could actually be a excess buildup of ice that is covering the thermostat and not totally melting during each cycle. I've not gotten close enough to the timer to see if it is mechanical or electronic. According to the diagram, it is inside the refrigerator compartment. If mechanical, I can check for broken or warn parts controlling the switch. I've got to remove some plastic first. I wish I had a spare refrigerator that I could keep things in while I dug into this one. Dwight

I've never encountered a defrost thermostat configured as you describe although I have to admit it's been a decade or two since I've replaced any defrost heating elements. And I would have to wonder what the need for such a device would be. The heating elements should be engineered to do their job in a specific amount of time being dictated by the duration of the defrost timer. I really don't see any need to introduce another control into the defrost circuit. Also, ice build up is always not uniform and placing such a device where the temp has achieved 32F while another part of the evaporator still had not defrosted completely isn't a good thing. Sorry Sam, just thinking out loud here ;)

the

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Well that blows my theory about not needing a defrost thermostat :) Honestly I've never seen one and I've replaced the defrost heating elements on maybe a dozen refrigerators. Maybe I just wasn't looking? Regardless in this case it seems a likely suspect per the symptoms you describe and certainly worth replacing.

Hi My understanding is that this is more related to the automatic detection of when enough defrost has completed. They'd place the thermostat somplace on the evaporator that was most likely to hold the most ice. This would most likely be imperically determined, based on specific air flow and such around the evaporator and heater location. From what I've seen in the catalogs, the timer is just the simple clock motor with switch contacts. Of course, it is in a plastic enclosure but the shape looks like a clock motor. Now, I wonder how hard it is going to be to get to the switch. I've not been able to get time when I can stash the cold items someplace while fiddling with the covers. I do hope I don't need to disturb the evaporator too much. The switch is cheap enough but if I break a seal, all is lost. From GE it is $15 from RepairClinic, it is $12.85. Of course, it might be a problem of a long term build up of ice that hasn't been completely melted over time and is blocking the thermostat. I don't think this is likely but still possible. When I dig into it, I'll look for this. Dwight

to

Please start a new posting with whatever you find, so we don't have to go back in time to find out what you find.

How can they assure that the same amount of ice buildup is being removed every time? No, there should be a defrost thermostat or else it would have to be timed to defrost the worst case, and cook the food as well. :)

I agree that it would have to be positioned so that most of the ice gets melted before it turns off. The evaporator is aluminum which is a relatively good conductor of heat so this may not be that difficult.

It's not something you're going to just come across as it will be buried in the evaporator coils. They do go bad, though failure of the timer is most common.

It's certainly present 20 or 30 year old fridges. I don't know if every frost-free fridge but certainly the ones I've seen.

I guess there are other ways of detecting that the ice has melted, such as by sensing that there is no more water dripping down.

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Under nominal conditions we're not talking a huge amount of ice. And it really doesn't take a lot of heat to melt what is there. But rethinking this, the defrost should occur rapidly enough to spare the frozen food too much temp change. Not good on the food to develop ice crystals.

Those that I have replaced heating elements in were always caked with ice so it's understandable that I may just have not seen a temp cutoff device.

Well the more I think about it the more sense it makes to heat the evaporator rapidly and control that heating with a temp switch. I've heard ice cracking while my fridge defrosts. More so in the summer when the humidity is up and the door is opened more often for cold drinks.

well...........

Auto defrost always creates a problem by lowering temperature to dangerous levels, especially when your in and out of it during a defrost cycle. Any slight change in the system can create even more problems. I always noted that ice cream is always softer after the defrost cycle. After I bought one of these USB loggers of temp and humidity, I monitored my current home refridgerator for several days, both in the freezer and refridgerator section. The defrost generally ran for about 45 minuites. Overall the refridgerator section remains more constant during my test. I also used the unit as I usually do. I wish they would have a warning lamp come on telling of the defrost cycle, and also be able to set the time of day it occurs.

greg

" snipped-for-privacy@hotmail.com" wrote in news:17472f62-5b6c- snipped-for-privacy@a35g2000prf.googlegroups.com:

Take your stuff out and wrap it well with several blankets(they will keep out heat as well as keeping it in).

If you have cold weather sleeping bags, they work well, the more layers, the better.

This will help keep it cool for long enough to trouble shoot the problem....IF you are quick.

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