Hi, I've read through a number of other posts with similar titles/issues and I think I know what's going on, but being OCD I'm hoping someone can confirm or contest my diagnosis.

Kenmore model no. 253.71822106 with freezer on top.
Left unplugged over the summer. Plugged back in, doesn't cool, not even a little.

Light turns on.
Evaporator fan runs.
Compressor runs smoothly (vibrates/hums quietly), gets hot to the touch but not so hot that it can't be touched.
Compressor runs constantly, doesn't cycle off and on. Makes sense because the fridge isn't cooling so the thermostat wouldn't be sending compressor a signal to shut off, right?
Condenser coils at the back of the fridge are room temp.
No condenser fan to check.
Temp control seems to work because I can use it to turn on and off the compressor/evaporator fan.
Larger copper tubing going from compressor slightly cool, but not much more than room temp.
Smaller diameter copper tubing coming from bottom of condenser coils and going into compressor quite hot.
When I shut off fridge using the temp control and listen to large copper tubing with a stethoscope, I hear gurgling as system depressurizes, which seems to indicate there is at least some freon in the system.
No frost buildup anywhere.
No blockage of ducts.
Everything is clean as a whistle.
Defrost timer appears to work because at one point the compressor and evaporator fan turned off while I was investigating things and I had to turn defrost timer knob at bottom of thermostat control housing clockwise a few clicks to get it running again.

Don't think it is the start relay because as I understand it the purpose of that device is to kickstart the compressor into running, and the compressor seems to be running fine.
Don't think it is the capacitor because as I understand it the purpose of the capacitor is to cycle the compressor on and off so as to maintain a constant temperature. Compressor hasn't cycled on and off during the times I've been present. Although since fridge isn't cooling at all, that situation probably just hasn't arisen yet.
Don't have an ampprobe to check the current draw of compressor, but still I'm thinking it is either a faulty compressor that isn't pressurizing the system (although why would the smaller tubing going back into the compressor be hot if that were the case?) or it is a lack of freon in the system.
Sealed system so uncertain how it could have lost freon without some sign of it on the floor or elsewhere, unless freon evaporates when it leaks out?

Any thoughts anyone?

Thanks so much!