Admiral freezer used, pluged it in and the temp droped to 5 deg
Them climed to 30 and has stayed there for the past week.
Seems like it is on constant defrost.

Is it worth looking at ?

Of course it's worth looking at. Deep freezers really don't have many moving parts. A good repairman can probably diagnose the problem in less than 15 minutes. If this is a self defrosting freezer then it could have 1 of 3 problems keeping it from properly freezing.

1. Defrost heater faulty.
2. Defrost limit switch faulty.
3. Defrost timer faulty.

Any appliance that has the defrost feature is basically the same whether it be a refrigerator or a deepfreezer. They all have those 3 components to make them work and defrost properly. Your Amana is no different.