Samsung SR-S2028CVW

I inherited one of these beasties as the previous house owner had built the kitchen around it and couldn’t get it out! It has given us almost 8 years of hassle free service but now suffers from the famous defrost problem. The defrost heater is integral with the evaporator (not as shown in the spares section) and the control thermistor is cable tied to the unit. If this is a 3k thermistor then the output is within acceptable limits – 1k ish at 50C and around 7k in ice. The heater wires (black and red?) show that the heater is as near continuity as makes no difference but of course this may be ok if it is a low voltage unit. With every thermistor there has to be a reference on the pcb so that could also be the problem. Obviously the unit is not worth a new evaporator with the associated recharge, and probably not worth a new PCB. Does anyone have definitive values for the thermistor and the heater? Thanks