Freezer works but Frig is warm
 

:confused: I have a 3 year old Amanna frig with the freezer on the bottom. The freezer works but the frig warms up. I noticed frost on the coils in the frezzer so I defrosted the frig. It worked fine for about 10 days and then frost built up in the freezer again, then the frig warmed up again. I'm not sure if this refrigerator has a defrost timer, defrost heaterand defrost thermostat or the newer electronically controled defrost system. Does anyone know? what might this defrost problem be.
Any help would be greatly appreciated.
Amanna Frig model number ABB2227DES