Compressor runs for long periods. Compressor runs for long periods and frost forms on the

Question

Compressor runs for long periods and frost forms on the evaporator but fridge takes ages to cool. Condenser fan running and fins are clear *but* the condenser and compressor are only just warm to the touch. The fridge is a top loader with good seals. This has only started happening the last few days. Could this be low refrigerant gas pressure?