Elecrolux ER 6822d

Hi,
I have an Electrolux ER 6822d Fridge Freezer that I would appreciate some advice on, please. Syptoms are – the compressor runs continuously on all but the very warmest setting of the thermostat, and the fridge appears to cool quite slowly. If I stop the compressor by turning the thermostat down to a warmer setting (less than 1), it is a couple of hours before the compressor comes back on again. It will cut in and out on a low setting and the air temperature then seems to be maintained at 7.5 – 8 degrees. However the freezer compartment is far too cold at around -32 degrees C!, when the compressor is running for long periods. The rear radiator is warm but not evenly warm. This is a single compressor model with a non – electronic thermostat (phial and contacts type). I would suspect low on gas except for the freezer temperature. Any advice appreciated with thanks