Help me complete my understanding - basics of fridge operation

Hi all,

So i've spent the past 2-3 months researching how to turn a commercial fridge into a dry aging fridge in my home. I recently purchased the fridge and have it, but before I really start with any modifications, I'd like to really understand what's happening. For reference, I'm working on a 2020 True GDM-12.

I've spent a good amount of time reading about how this works and watching videos and lessons on how to read wiring diagrams, but at this point, if my wife walks in on me one more time watching a YouTube class on refrigeration repair, things are going to start getting pretty awkward lol.

With that said, I was hoping someone could help fill in the blanks I have on the general mechanics of how the fridge works and also some gaps in my understanding of reading a wiring diagram (which I'll probably make a separate post about).

1. Basic Understanding:

• So I understand commercial fridges are a bit different in how they work versus cold plate fridges. They have compressors, evaporators, condensers, and expansion valves but differ in how the air is circulated.
  • I've taken some of the paneling off on my fridge. There's a fan on the top middle of the unit angled down and right behind that, in the top, and back center, is a set of coils which I believe are the evaporator coils. There is a copper tube that runs up the left side of the fridge to the evaporator coils, and the compressor and condenser, and capillary tubes are all below
• The compressor will take in low-pressure, cold refrigerant gaseous and will pressurize it, which according to the ideal gas law, will create high-pressure, and higher-temperature gas
• That hot gas form of the refrigerant will then pass through the condenser, and a fan will blow room temp air on it, which will cause it to condense and begin turning from gas to liquid and will reject some of the heat to the colder air in the room, cooling it down some (is this last part correct?)
• It then goes through the capillary tube, which changes the pressure and state again. Similar to an aerosol can, when you have a liquid passed through a pressure point into the larger open air, it will turn into a gas. And if you decrease pressure, you decrease temperature as well. This process happens in the capillary tube and now creates a cold, gaseous state of refrigerant, which is passed to the evaporator. Not all of the refrigerant is gaseous, some are still liquid.
• B/c hot air will want to travel to colder substances, the heat from the items inside the fridge gets drawn to the evaporator, which will cause the liquid refrigerant to boil/evaporate, which cools the gas and absorbs heat as it runs through the coils
• That cold gas then goes back to the compressor to get re-pressurized into a hot, high-pressure gas, and it repeats.

So first, is my understanding correct (and please fill in any gaps - this is just aggregated from many different sources, so I might still be missing some key concepts)?

If so, what is the purpose of the fan at the top of the fridge? Is it sucking air toward the evaporator from inside the fridge, or is the idea that it just generally circulates air by blowing down and pushing any hot air around to eventually find its way to the evaporator. (I only ask b/c when I put my hand up to it, I don't feel a ton of force unless I'm about 5-6inches away from it)

The only other main point of consideration is when it comes to humidity. I know there have been issues with freezing on the evaporator. Why does this happen? I know fridges generally run 70%+ humidity. If I put beef in there, it can get up to 90%+ in the initial stages. Is that extra humidity freezing on the evaporator, and it's just a matter of the fridge being able to handle 70% and not 90%?

Thank you so much for reading this novel. I (and more so my wife) thank everyone here very much for the information. Hopefully, wiring diagrams are easier to understand!

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