GE PFE28 bottom freezer. Unit is 4 years old. Freezer and reefer are both same temp, 41F. Fan in freezer runs intermittently. Condenser coil clean, condenser fan and compressor running. If I set reefer temp lower it does not get any colder. Portion of evap in freezer that is visible in back of freezer is about 39F, so that makes sense as to why reefer and freezer won't get much colder. But why isn't evap colder?