Frigadaire side-by-side not freezing/cooling

Freezer section pulls down to 20, fridge down to 48. Cleaned condensor coils and checked that compressor is running as well as both fans. Found evap coil with thick ice on it, replaced defrost thermostat. It didnt help, so found I could manually put into defrost mode. Compressor and fans stopped, and and damper closed. Had to manually take out of defrost mode. I’m thinking defrost control bad, but wonder if this is the main problem. Noticed that when it is running, there isnt much air coming through the damper into the fridge section. Temp control seems to be working. I can turn it down and you can hear it click and then close damper. Could it be low on refridgerant also ?