hot-wired a fridge mystery component. Nothing happened. What is it?

Submitted ⁨⁨4⁩ ⁨days⁩ ago⁩ by ⁨diyrebel@lemmy.dbzer0.com⁩ to ⁨fixing@slrpnk.net⁩

The thermostat is dead in my strange¹ fridge with no replacement parts. I posted about the mystery component before.

There is a metal plate that appears to sandwich a single small loop of refrigerant (guessing!). Mounted attached to the backside is a coil with a ground and two wires marked to handle 220v. One of the leads connects to the LOAD wire on house mains and the other to the (now broken) thermostat.

I can only imagine that it’s a heating element for defrosting. But I struggle a bit with that theory because I’m surprised the fridge would ever get cold enough to justify defrosting.

Anyway, I wired the mystery coil directly to mains and left it for 10 min or so. The temp of the metal plate did not feel any different. Is that expected? Metal is naturally cold at room temp and that did not change.

I would like to understand it because I cannabalised a simpler t-stat from another fridge. The t-stat has no connector for whatever the mystery component is… it’s just a switch that connects two wires. I don’t know if I should just omit the mystery component, or if I should wire it in series with the new t-stat, or keep it attached to the old broken t-stat and wire that in parallel to the new t-stat.

¹ I say strange because there is no freezer-fridge vent. So the fridge is independently cooled.

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vudu@slrpnk.net ⁨4⁩ ⁨days⁩ ago
A picture is worth a thousand words… What model fridge do you have? Let’s get some closeups of these components

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- diyrebel@lemmy.dbzer0.com ⁨3⁩ ⁨days⁩ ago
  I would really be hard-pressed to get a pic of the Zanussi 19/4 that’s worth 1k words in this situation. The backside of the plate is inaccessible. Every time I pull the plate forward to get an eyeball back there I worry that a tube carrying coolant will break.
  
  I found the manual online somewhere but it’s almost useless. Perhaps this excerpt is useful though:
  
  Defrosting
  
  Frost is automatically eliminated from the evaporator of the refrigerator compartment every time the motor compressor stops, during normal use. The defrost water drains out through a trough into a special container at the back of the appliance, over the motor compressor, where it evaporates.
  
  It is important to periodically clean the defrost water drain hole in the middle of the refrigerator compartment channel to prevent the water overflowing and dripping onto the food inside. Use the special cleaner provided, which you will find already inserted into the drain hole.
  
  The freezer compartment, however, will become progressively covered with frost. This should be removed with the special plastic scraper provided, whenever the thickness of the frost exceeds 4 mm.
  
  This is a pic of the front side of the metal plate: pic of metal plate in fridge compartment
  
  There are two white wires and a ground wire going from the blob on the right to behind the plate. The wires run in a loop inside some coil of tube.
  
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  - bitfucker@programming.dev ⁨3⁩ ⁨days⁩ ago
    Oh, it is a big plate. Probably not a thermal cutoff then
    
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bitfucker@programming.dev ⁨3⁩ ⁨days⁩ ago
It seems like I cannot find a picture of your component (if you ever posted any). If it is metallic looking, it is probably a thermal cutoff of some sort. The wikipedia article focuses on the fuse-looking one, but there also exists a flat metal plate looking one. The connection is usually normally open so if the temperature on the loop is ever too high, the motor (compressor) will trigger. The normally closed connection one is for motor overheat protection. That kind is usually placed/glued to the stator body, so if it ever gets too hot, it will stop the motor instead.

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- diyrebel@lemmy.dbzer0.com ⁨3⁩ ⁨days⁩ ago
  resistence measures at 14.15 kΩ
  
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  - bitfucker@programming.dev ⁨3⁩ ⁨days⁩ ago
    Ahh, probably a broken heater then. If it is a normally open thermal switch, it should not have that low of a resistance
    
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- diyrebel@lemmy.dbzer0.com ⁨3⁩ ⁨days⁩ ago
  I posted a pic in a reply but the component is hidden behind the metal plate.
  
  I wonder if it is a thermal fuse, then I don’t know what would warm the plate. It has a coil of refrigerant which you can see in the pic… just one loop of coolant. I’m baffled that it’s enough to cool the whole fridge compartment. As far as getting warm, I wonder if the compressor could somehow run in reverse and push hot refrigerant through the coil to defrost things?
  
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  - bitfucker@programming.dev ⁨3⁩ ⁨days⁩ ago
    I’ve seen the pic. So the plate is not the component? I thought the whole plate was the component. In that case, if it is a small metal plate like any of this, then it most likely is a thermal cutoff.
    
    Thermal switch variation
    
    It’s not running the compressor in reverse necessarily. It just used to sense when the temperature of some point has reached some threshold. Remember, a high temperature on the cold side could also be used to trigger the compressor to cool down the fridge.
    
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Nomad@infosec.pub ⁨3⁩ ⁨days⁩ ago
If this is indeed a non us fridge, this is probably a heat pump fridge. Compressor in the back should confirm it. The plate probably allows the coolant to expand and thereby cool down inside the fridge.

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- diyrebel@lemmy.dbzer0.com ⁨3⁩ ⁨days⁩ ago
  It’s a non-US fridge. But I’m curious about you calling it a heat pump fridge. The one thing all fridges have in common is using a compressor for refrigeration, which is the same as a heat pump but stressing that the goal is to cool rather than heat a space. Are there US fridges that do not use a compressor?
  
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  - moonshadow@slrpnk.net ⁨2⁩ ⁨days⁩ ago
    The only exception I’m aware of to all fridges having a compressor is propane models. There’s a vessel they heat to build pressure in its place, and sometimes an (incredibly inefficient) electric mode where a resistive heater acts on that vessel. They’re very uncommon, pretty much exclusively used off-grid, and in no way specific to the US.
    
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