Most fridge/freezers use only one compressor providing freezing to the freezer compartment. Cooling of the fridge section is achieved through a ducted air channel connecting the freezer and fridge compartments – with a small fan providing the air movement, together with a damper mechanism and vents into the fridge compartment.
If your fridge is of the above construction – mark sure that you have not blocked the fridge compartment air vents (normally located in the back of the fridge compartment).
Control of the temperature in the fridge compartment is achieved by a thermostat/controller, switching on/off the fan (as required) – any of which could be faulty.