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Defrost cycle frequency


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33 replies to this topic

#1 expat

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Posted 09 April 2005 - 04:23 AM

Hi Everyone,

A bit of preamble, 'cause I know people are going to suggest I contact the store I bought this product at. I live in Thailand and requesting warantee service here for this kind of subtle problem is a waste of time. They will just make excuses.

A few month ago we bought a new Mitsubishi refrigerator. The problem is that every single day the temperature goes up to almost 32 F for a hour or so. I assume it is defrosting, but every day? Ice cream gets mushy and I wonder about the safety of my other frozen foods. Actually it might even be more than once a day. If it happens in the middle of the night I would not know it. When it is operating normally, the temperature is fine close to 0 F in the freezer.

The question is, is this normal and if not is it just a question of changing the defrost timer?

Thanks for your ideas,

Peter

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#2 Samurai Appliance Repair Man

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Posted 09 April 2005 - 05:59 AM

Gotta love third world service.  Did some R&R in Thailand during my Navy years, nice people, beautiful women, plentiful recreational substances, but it didn't strike me as a place where workaholism was a wide-spread problem. 

No, your fridge problem is not normal, it should not get that warm during the defrost cycle.  It's either a design flaw or, more likely, just something wrong.  You should call Mitsubishi directly and insist that they pressure the local dealer to swap out this fridge with a new one.


#3 expat

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Posted 09 April 2005 - 04:41 PM

Hi Samurai,

Love your name and ad.

Good to know now that in fact this is not normal.

Now way Mitsubishi is going to give me a new unit. The only way this is going to be fixed is for me to explain to a repairman exactly what parts I need replaced and maybe even buy them myself because these repairmen are not really professional and the mindset here (as you may know already) is if it works it isn't broken.

Can you tell me:
- Is it normal for it to go into this cycle every day?
- About how warm _should_ it get?
- As an I.T. guy I know it is tough to diagnose by phone/email but what is the most likely cause? Defrost timer?

Thanks,

Peter

#4 Samurai Appliance Repair Man

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Posted 09 April 2005 - 05:00 PM

[user=167]expat[/user] wrote:

Can you tell me:
- Is it normal for it to go into this cycle every day?
- About how warm _should_ it get?
- As an I.T. guy I know it is tough to diagnose by phone/email but what is the most likely cause? Defrost timer?

If it's a straight mechanical defrost, it'll defrost every 6 to 8 hours for about 21 minutes.  If it's adaptive defrost, it'll defrost according to usage.  During defrost, compartment temp could rise 10 or so degrees F but the freezer compartment should never even approach 32F. 

A key piece of diagnostic information is whether or not the compressor is still running during the warming period.  If not, then the defrosting system is suspect, especially the defrost thermostat, also called the defrost terminator.

If the compressor is still running when this occurs, then the problem is moisture in the sealed system creating an ice plug in the evaporator at the point where the capillary tube is attached.  This ice plug blocks any further flow of refrigerant into the evaporator (located in the freezer) and causes the freezer to warm up to exactly 32F.


#5 expat

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Posted 09 April 2005 - 05:42 PM

Wow - thanks a lot for the detailed info.

Peter

#6 The Seven

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Posted 09 April 2005 - 08:58 PM

[user=167]expat[/user] wrote:

The problem is that every single day the temperature goes up to almost 32 F for a hour or so.

The question is, is this normal and if not is it just a question of changing the defrost timer?

Peter


Could you describe how did the temp change during the defrost cycle?

The attached JPG file shows an adaptive defrost cycle of an Sears fridge (GE Side-by-side).
During the defrost cycle, the temp of the freezer rams from pre-chill temp -16 F to 24 F in 30 min. Then it cools down from 24 F to 0 F in 50 min. The temp of the freezer above 10 F for about 40 min.

Attached Files


The Seven

#7 expat

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Posted 09 April 2005 - 10:31 PM

Hi Seven,

I did keep a spreadsheet over a daytime two day period which I am attaching. As you can see, the pattern it is not like the adaptive defrost at all.

I am going to check today if the compressor is on when it happens (therefore probably it will _not_ happen today!).

Thanks,

Peter

Attached Files



#8 The Seven

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Posted 09 April 2005 - 10:45 PM

Recently I did a temp measurement in my Kenmore top-freezer 18 cu ft fridge (over 10 years old). The defrost cycle is about 21 min for an cummulative run of 10 hour.

During the defrost cycle: the temperature of the freezer raises from 4 F to 28F in 20 min. Then it cools from 28 F to 4 F in 50 min. The temp is above 10 F for about 30 min.

My Kenmore (without adaptive defrost) is not much worse than the above GE (SxS) with adaptive defrost plus pre-chill.

Have any one else actually measured the freezer temp during the defrost cycle? Any better or worst?


The Seven

#9 Samurai Appliance Repair Man

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Posted 10 April 2005 - 03:11 AM

[user=7]The Seven[/user] wrote:

During the defrost cycle, the temp of the freezer rams from pre-chill temp -16 F to 24 F in 30 min. Then it cools down from 24 F to 0 F in 50 min. The temp of the freezer above 10 F for about 40 min.

Where did this data come from and what instrument was used?  I've made my own measurements in past using a Supco temperature data logger and did not record anywhere near that kind of temperature rise in the freezer during defrost.


#10 expat

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Posted 10 April 2005 - 03:50 AM

Guys,

I got a feeling this is kind of a silly question, but...why would the ice melt if the temperature does not go above freezing?

One more - is it normal for a compressor to run way to hot to touch?

Thanks again,

Peter

#11 The Seven

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Posted 10 April 2005 - 06:10 AM

[user=1]Samurai Appliance Repair Man[/user] wrote:

[user=7]The Seven[/user] wrote:

During the defrost cycle, the temp of the freezer rams from pre-chill temp -16 F to 24 F in 30 min. Then it cools down from 24 F to 0 F in 50 min. The temp of the freezer above 10 F for about 40 min.

Where did this data come from and what instrument was used?  I've made my own measurements in past using a Supco temperature data logger and did not record anywhere near that kind of temperature rise in the freezer during defrost.



My attached "image004.jpg" was taken from a "xmb_GE_Arctica_SxS.pdf" file from our old msn web-site. Page 9 on the topic of Pre-chill and Adaptive Defrost of the service manual of the GE_Arctica_SxS fridge. The data is interpreted from the JPG file.






The Seven

#12 The Seven

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Posted 10 April 2005 - 06:29 AM

[user=167]expat[/user] wrote:

Hi Seven,

I did keep a spreadsheet over a daytime two day period which I am attaching. As you can see, the pattern it is not like the adaptive defrost at all.

I am going to check today if the compressor is on when it happens (therefore probably it will _not_ happen today!).

Thanks,

Peter


Peter,

Your pattern is different because there is no "Pre-chill" in your fridge. My one has none too.

The Seven
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#13 The Seven

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Posted 10 April 2005 - 08:12 AM

[user=167]expat[/user] wrote:

but...why would the ice melt if the temperature does not go above freezing?
Peter


Peter,

You have a great enquiry mind. "why would the ice melt if the temperature does not go above freezing?" I would have the same query too.

Let us note the following illustration.
There are two objects in an enclosed chamber. One is at 100 C (HOT object) and the other is at -100 C (COLD object).

What is the (air) temperature inside this chamber?
Engineering speaking, the average temp is 0 C.

What would happen if an ice-cream is put inside this chamber? The part near the HOT object will melt and the part near the COLD object will still be frozen.

This may apply to the fridge during the defrost cycle.
The evaporator coil is normally housed in the freezer compartment separated by an evaporator cover. The defrost heater will heat up the evaporator section up to 50 to 70 F (most Kenmore use 70 F) to defrost the coil. If the evaporator cover will be also warm because it is usually a thin sheet of PVC or aluminium. Most of the food in the freezer is about 0 F.
What would be the air temp inside the freezer section at this time? Engineering speaking, the average temp could be 20 to 30 F.
Would the ice-cream partly melt? Now you have the answer.

My comment to "If the evaporator cover will be also warm because it is usually a thin sheet of PVC or aluminium." My Kenmore uses alumunium evaporator cover which is the worst. The alumunium cover is a very good conductor of heat and its temp would be close to 50-70 F. More heating energy is needed to heat the evaporator section and the poor insulated cover/food. More cooling energy is needed to cool the food back. More energy is wasted. It is a poor engineering design.

Some models use thin PVC cover but they are not much better. A better engineering design should use an evaporator cover which is properly "insulated". It seems that there isn't any fridge using the "insulated" evaporator cover.

The Seven

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#14 Moostafa

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Posted 10 April 2005 - 02:36 PM

Hello, my unchilled friends.  May I interject?  I submit that these defrost problems could be avoided if you purchased a nice Muslim refrigerator, such as the Kiriazi.

Posted Image

It is a fine, Egyptian-built refrigerator that is used extensively here in Afghanistan.  Its performance in these harsh desert conditions with wide variations in ambient temperatures has been exemplary.  For example, summer days can reach > 105F and the nights can get down to 31F.  Since the Kiriazis are kept in our open-air tents, they are exposed to the wide swings in ambient temperature.  I am here to swear before Allah and upon the eyes of my dear mother that freezer temperature never rose above +20F.  We monitor this scrupulously because we store semen specimens from our prize-winning yaks in the freezer and they must be kept under the strictest temperature control or else they lose motility. 

I pray that my comments added something to your discussion.  Please, go back to what you were talking about.

Allahu Akbar!


#15 The Seven

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Posted 10 April 2005 - 03:55 PM

[user=167]expat[/user] wrote:

One more - is it normal for a compressor to run way to hot to touch?

Peter


Peter,

From Embraco website, most new compressor-motors are designed to work up to 140 F. Can your hand stand that temp?

Hope your queries are clarified.

The Seven
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#16 Budget Appliance Repair

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Posted 10 April 2005 - 11:42 PM

Surprising, noone has mentioned the possiblity of a bad "Defrost t-stat/terminator".

IF the "Defrost terminator" has failed, contact points welded together, you would have the defrost heater on the full length of defrost, aprox. 21 minutes. Which would allow the freezer temp to spike to these high temps and the ice to melt.

William Burk (Willie)
Willie's Budget Appliance Repair
Eureka, CA 95501
William Burk (Willie)
Willie's Budget Appliance Repair
Eureka, CA 95501

#17 expat

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Posted 11 April 2005 - 03:57 AM

Shalom Moostafa!

I was in your wonderful country about 30 years ago. I remember well the quaint plumbing. You know, how the balconies hang over the alleys and there is a hole cut in the floor and that is the sewage system. Gravity does the rest! Allah help the poor Afgani that mistakenly takes an alley for a shortcut, though, because then they really step in it, eh? Hey, I bet you don't get many service calls for blocked toilets ...hehehe....

And then there were the beautiful Afghani women in those cute peek-a-boo burkhas, or maybe is was the beautiful Afghani goats? Anyway, one or the other!

Seriously, though, the best thing was... ah, ummm.. well it'll come to me soon....

#18 The Seven

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Posted 11 April 2005 - 04:30 AM

[user=36]Budget Appliance Repair[/user] wrote:

IF the "Defrost terminator" has failed, contact points welded together, you would have the defrost heater on the full length of defrost, aprox. 21 minutes. Which would allow the freezer temp to spike to these high temps and the ice to melt.



Thanks Willie for the input.

The defrost heater is ON for about 14 min (not the full-time) during the 21 min defrost cycle. The heater takes about 4 A. The defrost function was checked OK.

Please note that the GE_Arctica_SxS fridge as stated in its service manual has a similar temp spike. This GE and my Kenmore uses 60-70 F as defrost terminating temperature.

During the defrost cycle, the evaporator coil section reaches a temp of about 70 F and the freezer food has a temp of about 0 F. They are separated by an alumunium evaporator cover.

What then would the air temp of the freezer food section be? Please do your experiment to find out.

The "air" temp inside the freezer could be measured easily by an "Indoor/Outdoor digital" thermometer. Please do not put the "Outdoor" sensor inside the frozen meat to obtain the "air" temp.

The Seven


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#19 GuidofromCT

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Posted 12 April 2005 - 03:24 PM

Hey peter,

Is the freezer full??? More food in freezer translates to less warming during defrost.

Just a thought.

yo, just do what ya gotta do!

#20 The Seven

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Posted 12 April 2005 - 05:21 PM

[user=216]GuidofromCT[/user] wrote:

More food in freezer translates to less warming during defrost.

Just a thought.


Good thought - Agreed.:D



The Seven




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