could be a multitude of sins that cause this.Low gas content in system,poor pumping compressor,faulty defrost heater,fault temperature sensors.No easy way to diagnose these unless you test each component.defrost for 24hrs totally and then retry.if it runs then but fails to get to temperature suspect compressor/gas issue (very expensive repair).if it seems to work ok but fails in a months time suspect defrost heater/temperature sensors (£100 ish).This is only a customer test guide not a 100% diagnoses!
ck
October 2009