the ice build on the inside rear panel does indicate a problem with the heater circuit.if the f/freezer was opperating correctly the ice would be in a bead formation/frozen dots of ice covering the rear panel.at preset times the heater circuit cuts in,the compressor is disabled and the frozen beads of ice turn to water ,and then run down the rear panel,into the drainage channel ,through the bottom of the fridge via a pipe which connect to the evap tray ontop of the compressor.the water is then evaporated by the heat generated by the compressor.your heater circuit has failed ,hence the large build up of ice.you could try replacing the pcb/electronic T/stat.as this will also control the initiation of the heater circuit.I have had a look around various websites and have not been successful locating the pcb.I know two versions of the rd were manufactured,one for the uk market.now that your f/freezer has had a full 24 hour defrost I would refit old pcb and boot the f/freezer up.see how it goes.your f/freezer is quite a old model now .a repair to the heater/filter and regass in my opinion not worth it.also check the doorseal around the fridge door for condition,the seal should be sealed correctly all the way around and no splits,.check the door for total closure,any gaps splits food debris can impeed the door closure.that can cause the compressor to run and override the evap/timer/filter.same effect of leaving the door open all night.whatever you decide to do I wish you gud look.
mech monster
November 2011