CDA PC50SC fridge freezer

I have a CDA PC50SE American-style fridge freezer, which I bought with a known problem (for £1, so I decided it had to be worth a punt). When it’s first plugged in, it starts up properly, compressor sounds smooth and quiet, and everything gets lovely and cold. After a day or so, however, it defrosts and can only be made to work by unplugging it for a few hours and starting again. I’ve never stood next to it for long enough to ascertain whether the compressor is cycling normally, or whether it cuts out once and never starts again, although I’ve noticed that when it’s in use, it soon gets too hot to touch. Not sure whether this is normal or not. Can anyone suggest some tests I can try to find the problem? Thanks!