true but depending on the refridgeration system type a slightly under gases system will cause extended compressor running time hence the fridge will get too cold.also uneven frosting or ice build up on the backwall/evaporator is a indication of loss of gas.

mechanical thermostats either work or they dont,usually go open circuit,ive never had one go out of calibration

if the system runs on a pcb/thermistors set up you will have to get the resistence values from the manufacturer to test the thermistors