GE Refrigerator is warm but freezer is cold

[Nick1971]

Hi-my refrigerator has been getting gradually warmer for the past week, but the freezer is cold. I pulled off the cover in the freezer today and saw that the coils were totally covered in ice and frost. I got rid of the frost with a hair dryer and went out and got a new themostat and installed it and now the freezer is working and the refrigerator cooling down again. How can I verify that the timer and/or the heater are working correctly? I just guessed on the thermostat. I assume that it is cooling down because I manually removed the ice (I really need to know if this is going to work because I store my son's medication in the fridge and it is $1500.00 a box and I already had one box ruined this week because of the gradual increase in temperature.)

Thanks to anyone who can tell me how to check the timer and heater-
Nick

Model TBX22zABLRWW

[JWWebster]

Most of the time it is the heater specially  the glass encased type. The newer models come with a harness, a defrost thermostat. and the qiock connect. Nothing to it me bucko.