My Kenmore 15 chest freezer (about 20 years old) is only cooling to 39F degrees. I defrosted it and no change. I bypassed the thermostat by plugging a wire to join the two terminals that plug into the thermostat and no change. The seal on the top lid is good. Thoughts that come to me are that it could be a compressor problem etc. - that is, things that aren't worth fixing as compared to just replacing with a used unit. My question is is there any reasonably likely problem going on here that is fairly easy and not expensive to fix?