Your refrigerator's defrost system may be the cause of the frost buildup on the inside back panel and the higher temperatures in the refrigerator compartment.
To resolve the issue, you can take the following actions:
Check the thermostat for defrosting: Once the coils have reached a certain temperature, it is the job of the defrost thermostat to turn off the heater. It may not be turning off the heater, resulting in excessive frost buildup, if the thermostat is defective.
Using a multimeter, you can check the thermostat for continuity.
Check the heater that defrosts: During the defrost cycle, the defrost heater melts the accumulated frost on the coils. It's possible that the heater won't be able to melt the frost, resulting in its accumulation. Using a multimeter, you can check the heater for continuity.
Check the defrost control board and timer: The defrost cycle is started on a regular basis by the defrost timer or control board. It's possible that the defrost cycle is not being initiated, resulting in frost buildup, if the timer or control board is defective. Using a multimeter, you can check for continuity on the control board or timer.
And if the above is not helpful, do try the ones below;
Check the thermostat for defrosting: On the evaporator coils in the freezer compartment, you'll find the defrost thermostat. Once the coils have reached a certain temperature, it shuts off the defrost heater. Use a multimeter and disconnect the wires to test the thermostat at room temperature for continuity. The thermostat is faulty and must be replaced if there is no continuity , you can replace with https://amzn.to/3lvYEAy.
Check the heater that defrosts: In the freezer compartment, the defrost heater can be found on the evaporator coils. During the defrost cycle, it melts the accumulation of frost on the coils. Use a multimeter to verify continuity while disconnecting the heater's wires for testing. The heater is defective and needs to be replaced if there is no continuity with a new one that can be found on https://amzn.to/3lui4pr.
Check the defrost control board and timer: Behind the toe kick panel or inside the control panel at the top of the refrigerator is where you'll find the defrost timer or control board. It is in charge of periodically starting the defrost cycle. Using a multimeter at room temperature, check for continuity when testing the timer or control board. The timer or control board is broken and needs to be replaced with a new control board and timer via https://amzn.to/3I0j2Bn
Examine the door seal: Warm air from the outside can enter the refrigerator and cause frost buildup on the coils if the door gasket is damaged or not sealing properly. Check the gasket for any signs of wear or damage, and if necessary, replace it.