hotpoint FF200 eg evap iced up

hi all , just at this f/f today , completely blocked with ice from the top of the pipes to the bottom of the freezer compartment , i used the hairdryer technique (half an hour later] and i was able to get at the defrost element wiring there is a white square sensor block sitting under the start of the evap coils and two more wires going to the defrost heater , i checked the wires going to the heater 348 ohms resistance and the two pairs (yellow and blue ) going to the sensor block 27 ohms and 24.8 ohms respectively , there are 2 more cylinder type sensors one at the top of the evap coil and one at the bottom of the coil couldnt test these as i couldnt see where they went numbers on rating plate are ind. 7640732 and s/n 608140-152 does anybody have a technical sheet or diagnostics on this model i see a few posts about this problemish , but no answers thankya