Confused over frozen evaporator coil

[FCold]

Hi everyone,

Got an issue with a freezer I'm dealing with. Problem is the top half freezes over solid.

1) The evaporator fan is running.
2) The evaporator heating element gets very hot however cannot defrost the solid ice at top of coil.
3) Defrost is activated 5 times daily and comes on and off, correctly.
4) R404A charge is exact.

Thanks.

[chemi-cool]

Are the heating elements at the bottom only or also in the middle of the coil?
Is the coil clean?
Where about in the coil is the defrost sensor?
How long is the defrost cycle?

[FCold]

Heating element is clipped to the bottom of evap coil, there's none in the middle. Also the coil is very clean.

NTC probe is located near top inside evap coil and replaced for new recently.

Defrost cycle last for around 30mins.

[chemi-cool]

If the coil is not too high, it should be OK, set the defrost termination temp to 8C

[smpsmp45]

Generally such coils have heaters right in the coil surface from top to bottom. If the heaters are at the bottom only, it is difficult to get rid of such ice formation.
Just check the possibility of using rod heaters at the top level generally inserted in the finned surface