No Frost Fridge

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Anonymous Poster	No Frost Fridge 11/09/2008 1:03 AM
	About "No Frost" fridge. Is it possible to make a direct switch for the defrost heater? I think the defrost timer is no longer working. What I am planning to do is to turn the motor off and switch on the heater manually for maybe an hour or less to defrost the freezer. The problem is, there is no available parts here in this country where I am staying right now. Can anyone help me pls? thanks
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Circuit Breaker Guru Join Date: Jul 2006 Location: CA (Central Arkansas, USA) Posts: 599 Good Answers: 10	#1 Re: No Frost Fridge 11/10/2008 9:02 AM
	A defrost clock for a residential refrigerator is just a single pole double throw swith flpped by a motor. In the cool mode the compressor, condensor fan and evaporator fan are powered (the compressor and condensor fan through the thermostst). In the defrost position the above parts are de-energised and the defrost heater(s) are energised. I seems like any medium duty switch should be able to do this. Also there are many generic defrost timers available. They are sold based in the number of defrosts per day and the maximum lenght of the defrost cycle. It seems like you should be able to mail order one fairly easily. -- JHF __________________ If it's too good to be true, it probably isn't
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Brave Sir Robin Guru Join Date: May 2007 Location: Annapolis, Maryland Posts: 7940 Good Answers: 458	#2 Re: No Frost Fridge 11/10/2008 11:45 AM
	Wouldn't it be more efficient to put a thermostatic switch on the evaporator, such that when the compressor is off, the heater is on if the temperature is below 4 C or something like that? Thought process is that we don't power the heater if we have already melted the ice off of the coil.
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Anonymous Poster	#3 Re: No Frost Fridge 11/10/2008 4:49 PM
	Do not attempt to modify the electrical design of your refrigerator for safety reasons! Electrical shorts may occur causing structural damage and loss of life.
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Brave Sir Robin Guru Join Date: May 2007 Location: Annapolis, Maryland Posts: 7940 Good Answers: 458	#4 In reply to #3 Re: No Frost Fridge 11/10/2008 5:05 PM
	We have to assume that the readers of this forum will exercise good judgement as to their skills and knowledge. I wouldn't tell readers of this forum to look both ways before crossing the street. Certainly, I would hope that a refrigerator designer would not just install a timer switch that is based only on time. That would mean that the refrigerator would have to be designed for worst case conditions (humid) where the greatest moisture rejection (evaporator icing) would occur. In drier environments, the heater would run unnecessarily long and waste energy. Cheers !!
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Circuit Breaker Guru Join Date: Jul 2006 Location: CA (Central Arkansas, USA) Posts: 599 Good Answers: 10	#5 In reply to #4 Re: No Frost Fridge 11/10/2008 5:16 PM
	That is the way most residential refrigerators work but with one more part I didn't mention in my previous post. There is a limit thermostat in series with the defrost heater that turns it off when the temp is high enough that all the frost should be melted, but the defrost cycle on most home refrigerators is time controlled, not demand controlled. Some high end refrigerators use some sort of demand control, but these always have a lot of problems. -- JHF __________________ If it's too good to be true, it probably isn't
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Brave Sir Robin Guru Join Date: May 2007 Location: Annapolis, Maryland Posts: 7940 Good Answers: 458	#6 In reply to #5 Re: No Frost Fridge 11/10/2008 5:45 PM
	I suppose you could place a DP sensor across the evaporator to sense icing. That could be used to cycle off the compressor and let the heater work until the temp sensor gets above the freezing point, then re-start the compressor if you haven't met the set point of the fridge. I guess what you are saying is that demand control is such that the controller "knows" there is icing, versus a "dumb" controller that "assumes" there is icing and turns on the heater and waits for a set time to elapse or the series thermostat to open the heater circuit.
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OlympiaWA Power-User Join Date: May 2008 Location: Olympia, WA Posts: 125 Good Answers: 5	#7 Re: No Frost Fridge 11/10/2008 8:51 PM
	Greetings. Usually if ice is building up on the freezer the defrost thermostat is defective. It is in line with the defrost heater. One side of the defrost thermostat has 120 volts on it at all times. The neutral is switched through the defrost timer. Usually the defrost timer is less than $20.00 and the defrost thermostat is less than $15.00. The defrost heater can be tested with a multimeter to see if there is continuity. Get the make, model, serial number, and manufacturing number if listed and call a repair shop in your area. They will sell you the parts. They are relatively easy to replace.
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msm98lw Power-User Join Date: Sep 2008 Location: Danbury, CT, USA Posts: 103 Good Answers: 2	#8 Re: No Frost Fridge 11/11/2008 5:50 PM
	Many years ago I had the defrost control fail on my fridge. I got the model of the fridge and ordered a new defrost control. It went in very easily. Turned out a wire had broken, so it would have been easy to fix without buying a new part. It's not worth jury rigging a solution. Replace the control. __________________ 6 * 9 = 42 in base 13
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Anonymous Poster (1); Brave Sir Robin (3); Circuit Breaker (2); msm98lw (1); OlympiaWA (1)

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