I went out to this about 8 months ago and defrosted the freezer, it has now frozen up again, I was going to fit new defrost sensor but any advise gladly received.
You can run a test program on it.
Switch off, press and hold the super freeze button and switch it back on holding the super freeze until P0 is displayed.
P0 starts a defrost phase
P1 FC fan
P2 RC fan
P3 Drain heater switched on
P4 Defrost heater switched on
P5 RC heater switched on
P6 Compressor runs
P7 RCS temp displayed
P8 No function
P9 FCES temperature displayed
P10 Status of FC door