Fridge on my fridger/freezer freezes up

We had the same thing at home recently, although ours was a fridge/freezer that we have had for 10years. Spoke to appliance repair engineer and he said there is possibly a small hole somewhere allowing the frezing air to collect at the back of the fridge. No answer though on how to fix other than replace.

An inexpensive, though inconvenient, way to determine if the problem is with the self-defrosting system, is to remove all of the perishable food from the refrigerator and freezer, turn the thermostat in the refrigerator to Off, and leave the doors open for 24 to 48 hours. (Be sure to have several towels ready in case the melting frost and ice causes the drip pan to overflow). This allows the refrigerator to defrost "manually." When the frost and ice build-up has completely melted away, turn the thermostat back to a normal setting. If the refrigerator then cools properly, it indicates a problem with one of three components in the self-defrosting system: The defrost timer The defrost thermostat (also called the bi-metal switch) The defrost heater If it still does not cool properly, there may be a problem with the refrigerant level or the compressor and you'd probably need to consult with a qualified appliance repair technician to further diagnose the problem, hope this helps.