Bottom Freezer - Fridge not cooling freezer okay

The freezer is cooling and but not the fridge main compartment. A repair person checked and replaced the mother board ($300) and the fridge worked for just over a week.

I am able to warm up the fridge till the freeze around the back of the freezer is thawed and fridge works fine for a week more or so.

Browsing through the web looks like I need to change the temperature sensor, but I am not sure how to get to the evaporator assembly. ANy help is appreciated

PFS22SBSSS is a Canadian MODEL Number, US model closest is PFS22SBSASS.

Thanks

George

Most probable problem is the defrost heater. Remove the freezer back panel, defrost the coils and check the heater, if black inside with a gap, it’s blown.

Thanks will check this week end