The temperature in my freezer compartment varies between 0 (the set point) and 10. In the fridge, it varies between 37 (set point) and 52 (over temp alarm). I've replaced the evaporator motor, fan blade and plastic support (motor was probably OK originally) because of a loud noise. It helped the noise some, but temps still vary. The diagnostic tests all show "1".

I have a very good repair manual and would like to test some components, but I don't know where to look. Since this is, I suspect, a partial failure, it may be that testing voltages and resistances will not show much. Could it be a coolant problem? Should I test the inverter/compressor?

Here is a thread in another forum where the problem is very similar, but the solution seems not relevant:

Kitchenaid KSSC48QMS Built in not regulating temp

Here's another thread about the evap fan/motor:
FIXED Loud noise from the freezer compartment

Here's another thread about suggestions made about this problem:
Kitchenaid-KSSC48FMS02-Built-in-not-regulating-temp revisited.

Any help is appreciated.