Not sure what they would be at the coldest settings.Most units when set to mid-scale should be:
Freezer: 0 to 5 degrees F.
Fresh Food around 40 degrees F.

If both are OK then it does not tell you that defrost is OK as it will take several days to a week or so for a defrost problem to show up. Usually you will notice the fresh food side getting warmer and later that the food in the freezer is melting. Also the compressor will fun all the time and not cycle like it should.

[COLOR="Blue"]My understanding is the compressor is located under the fridge. Is there a good way to tell it is running other than just listening?[/COLOR]
You should be able to feel it vibrating.

[COLOR="Blue"]For instance if I turn the fridge off(via temp control) to turn off the fan in the back of the freezer blowing air into the fridge then listening for a motor, would that be a good test, or is it associated with something else like the fan in the back side of the fridge running?[/COLOR]
No.
Turning off the unit will turn off the compressor.
Also the condenser/compressor fan is wired in parallel with the compressor so when one is on the other should be on.