need feedback on minifridge

[goldenmountain]

I would like to get some feedback on a mini fridge in the place I am renting, brand name is Kolin. It looks pretty old to me, so I want to verify it is functioning properly.

When I first arrived there was a very thick covering ice on the back of the fridge. I was advised to turn the fridge dial down to 2 so it would melt. I did this, and it did seem to melt; I thought maybe things were fine. But I put a grapefruit in there and part of it nearest to the back froze. When I looked inside the fridge i noticed the frost layer had returned.

So this time I unplugged the fridge and made sure it totally defrosted. No frost on the back at all. Plugged it back in - within two hours the frost was back, a thinner layer, but still a layer of frost on the back of the fridge. Is this normal for this type of fridge, and you just have to avoid putting things to close to the back or they will freeze? Or should I be able to store food at any location in the fridge without it freezing, if it's working properly?

Another thing I'm confused about: they sent a handyman who told me that I should keep the fridge dial on 2-3, so frost doesn't accumulate. I did that but it seems way too warm - the food and water in the fridge does not get cold enough on that temp. So I turned the dial up to 5 and that seems much better. Water I keep in the door is nice and cold.  I'm not sure of exact temp because all I have as an infrared  gun, but using that on various items on the fridge it tells me temps are between 45-50 on everything I tried. Seems too high -  but I don't know how well an infrared gun can gauge internal fridge temp though.

My main concerns here are the temp they are telling me to keep the fridge at seems too warm to be safe; but if I turn it up higher to like 5-6, I'm concerned I'm going to end up with more food freezing and getting ruined like the grapefruit. I don't know enough about mini fridges to know if this is normal for this type of fridge or these are signs the fridge needs to be replaced.