Fridge section not cooling but the freezer is fine — what's wrong?

Freezer cold + fridge warm is a classic airflow problem, not low refrigerant. In most fridges the cold air is made in the freezer and blown into the fridge section — if that path is blocked, the freezer stays cold while the fridge warms up. Check:

1. Frosted evaporator / blocked vents. Ice building up over the vents between freezer and fridge stops the airflow. Look for frost around the internal vents.
2. Defrost system failure. If the auto-defrost (heater, timer or sensor) fails, frost accumulates and chokes airflow — the most common cause of this exact symptom.
3. Evaporator fan. If the fan that pushes cold air into the fridge has failed, the fridge won't cool. Listen for it running.
4. Damper stuck closed between the compartments.

A manual defrost (unplug 24h) often confirms it — if it works afterward, then warms up again in a day or two, it's the defrost system. Cheap technician fix.