Freezer and fridge not cooling

There is heavy frost at the bottom of the freezer section and both the fridge and freezer sections are not cooling properly. A repairman changed the fan and thermistor to no avail. The fan would sometimes be heard operating and sometimes not. I have read and got a sound understanding of what to check for with regards to the fan supply voltages and I am yet still to actually check for myself. I would like to know what the resistances are for the thermistor for this model fridge at the different temperatures and also get a copy of a wiring diagram. Any other assistance will be appreciated.