Chest freezer problem

I have a chest freezer–Fricon THG 6S GILF–bought off Craig’s List for $75 seven years ago. It has a metal box inside on one side, rising around 1/4 the height of the interior and filling maybe 1/3 of the bottom. The compressor and fans are located inside that box, but there is no fan blowing into the interior of the chest.

It has mostly worked all this time (but things placed on the bottom near the compressor box froze poorly.) Thick frost builds up along all the interior walls and the lid. But a few days ago, everything began melting until there was little if any frost left. I moved all the (luckily, not much) thawing food into the top of my refrigerator.

Now, after a few days, it it is still not cold enough inside to freeze anything except at the top few inches of the interior. In those few days, inches-thick frost has formed again. I had placed several bottles of water inside to test the freezing in several parts, and one touching that area of frost is the only bottle slowly freezing. The compressor still switches on periodically and sometimes I can hear a fan faintly without the compressor on. The two exhaust vents are still warm.

So, any ideas what is going on? I don’t understand how it is freezing at the top but not the bottom–seems contradictory to heat rising, and to the lid being the least insulated part.

Sometimes there’s no answer that can be found, it’s just old. The stove in my apartment makes a loud banging/popping sound randomly a couple times a day or night. It does it even if I haven’t used it which makes no sense. It’s just old.

SWAG
it may have a leak and is loosing refrigerant. If the evaporator lines run from the top of the box to the bottom and the back to the compressor the top walls will be colder. Cold liquid refrigerant enters at the top and begins to pick up heat from the box and turn into liquid. If the only thing going through the lower lines is gas refrigerant then it will not remove much heat.

Repairing a leak on a old unit is not worth the expense. Time to get a new unit.