A fridge that runs but won't cool usually has a blocked airflow or heat-rejection problem — dirty condenser coils, a frosted-over evaporator fan, or, surprisingly often, an accidental demo/showroom mode.
A refrigerator cools by moving heat out through condenser coils and circulating cold air with an evaporator fan. The most common failures choke one of those: caked coils that can't shed heat, a frosted evaporator that blocks airflow, or a control set to demo mode that disables cooling entirely.
Check these in order. The first accounts for most cases.
Dust and pet hair coat the coils underneath or behind the fridge, so it can't reject heat. The compressor runs nonstop but nothing gets cold.
Many fridges have a store display mode that disables cooling. It's switched on accidentally more often than people expect — the panel lights work but the compressor won't cool.
If the defrost system fails, the evaporator coils ice over and the fan can't push cold air — the freezer may stay cold while the fridge section warms.
A failed compressor start relay or a sealed-system leak stops cooling entirely; both need a technician.
Follow these in order. Stop as soon as the problem clears.
Check the display for 'OF OF', 'O FF', or a demo indicator. Exit per your model (often holding two panel buttons 3–5 seconds). This costs nothing and fixes a surprising number of 'dead' fridges.
Unplug, find the coils (behind a kick plate or on the back), and vacuum/brush them clean. Restore a few inches of clearance around the fridge.
Make sure interior vents between freezer and fridge aren't blocked by food, and that the fridge isn't overpacked.
If the freezer is cold but the fridge is warm, a frosted evaporator or dead evap fan is likely. You may hear no fan, or see ice buildup on the back freezer panel.
Unplug, pull the relay off the side of the compressor, and shake it — a rattle means it's failed. Replacing the relay is inexpensive if that's the cause.