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 (as suggested). 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.

  • bitfucker@programming.dev
    2·
    8 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 thbe e stator body, so if it ever gets too hot, it will stop the motor instead.

    Edit: The picture provides a clearer size of the metal plate. A plate of that size is not a thermal cutoff. I don’t know what it is either. But if it is indeed a heater, you should be able to measure the resistance. If it is a resistive heater, usually it will have a low resistance (usually <10R). And metal is not “cold” at room temps, they are the temperature of room temps. It just feels cold because of higher thermal conductivity

      • bitfucker@programming.dev
        3·
        8 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

    • diyrebel@lemmy.dbzer0.comOPEnglish
      1·
      8 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?

      • bitfucker@programming.dev
        2·
        8 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.

        • diyrebel@lemmy.dbzer0.comOPEnglish
          1·
          8 days ago

          The mystery component is hiding behind the plate. If I follow the two white wires from the thermostat, they go behind the plate and make a loop that attaches to the backside of the plate.

          I mean, you could also say the plate is a mystery to me as well. I’m quite baffled by this fridge because it’s nothing like the videos I’ve seen on fridges. The plate must be cooling the fridge compartment because there is no vent coming from the freezer.

          I should mention that the /load/ wire that the mystery component connects to is the /return/ load going to the compressor. But that connection jumps to the t-stat. So I think it cannot be a cut-off because it’s wired in parallel to the compressor’s load input.

          So from how it’s wired, I think it’s expected to be a heating element. But it’s not warming the plate when hotwired. So maybe is a broken heating element… but yet it has continuity (14.15 kΩ). So I am baffled for sure.

          I guess I can only hope that someone has seen this bizarre Zanussi/AEG design before.

          • bitfucker@programming.dev
            2·
            8 days ago

            Yeah, that’s a broken heater. A broken heater sign is usually high resistance or good ol disconnect. It being in parallel further reinforces that. This is a common schematic for domestic refrigerators.

            Domestic refrigerator schematic

            • diyrebel@lemmy.dbzer0.comOPEnglish
              1·
              8 days ago

              For the moment I just disconnected the heating element and wired in a t-stat from a mini fridge. The heatin element could very well have been broken as long as I owned the fridge (it was given to me as a quite old 2nd hand fridge).

              I guess I will keep my eye out for similar normal sized fridges that are trashed. Maybe I can harvest a heating element and combined t-stat like mine to recover the auto-defrosting function.