No frost visible. There is a steady mechanical hum from the back panel which ceases when I turn the Freezer button to the Off position. So I assume that is the fan, and it is running.

Ok, hang on a bit. I get back to you in a few minutes. Thanks.

Lower panel is off. Fan is running. Compressor: how do I tell for sure? There is a noise, seemingly separate from the fan, in the unit on the other side of the fan (to the left, looking from the back of the frig). I touched the copper tubes on the right side of the fan. There are quite warm. Experiment: the Freezer cooling level has alwasy been set to 4. About 45 min. ago, I turned the Freezer knob first to zero (to listen), then to 7. I put a small plastic container half-full of water in the freezer. Maybe 4 oz. of fluid. I see that ice is just now beginning to form in the container. Also, when I pulled off the back panel, I saw a very thick layer dust around the fan, compressor, and pipes. I wonder if that's a factor. That area of the refrig hasn't been cleaned in 13 yrs. Ok, what next?