DIAGNOSIS A constantly running compressor usually means it's struggling to reach temperature. The top culprits are: poor ventilation (it's overheating), a warm room, a faulty door seal letting cold air out, or the thermostat is set too cold.
FIX Go through this checklist. 1) Ventilation: Pull it out from the wall. It needs at least 2-3 inches of space on all sides, especially the back where the condenser coils are, to breathe. 2) Location: Is it in a hot garage or next to an oven? Ambient temperature above 110°F can cause this. 3) Door Seal: Close the door on a dollar bill. If you can pull it out easily, the seal is weak. Clean the gasket with warm soapy water—dirt can break the seal. 4) Thermostat: Turn the dial from the coldest setting back to a mid-point (like 3 or 4).
IF THAT DIDN'T WORK If all conditions are good and it still runs non-stop, the thermostat itself might be stuck in the "on" position or the compressor's run capacitor might be weak, preventing it from building proper pressure to cycle off.
HEADS UP A fridge that runs constantly will have a shortened lifespan and a much higher energy bill. It's worth taking the time to troubleshoot the simple stuff first. Listen—if it's running but not actually getting very cold, that points to the more serious cooling system failure mentioned earlier.