What FD Means
FD on a Bosch French door refrigerator is the freezer defrost sensor, which the repair manual locates on the evaporator itself. It reports either a disconnection or a short, and it matters more than an ordinary temperature probe because the defrost cycle is timed against what this sensor reads. A freezer that is slowly filling with frost while still feeling cold is the symptom that usually accompanies it.
Common Causes of FD
- Freezer defrost sensor on the evaporator failed or shorted
- Connector at the main board unseated
- Harness damaged where it leaves the evaporator compartment
🔧 One Safe Check You Can Try
Look at the back wall of the freezer for frost building up in a sheet rather than the usual light dusting. Clear the compartment of anything blocking the return air vents and give it a day, but do not attempt to defrost it with a heat source.
⚠ Why You Shouldn't Go Further Than That
- The sensor is clipped to the evaporator behind the rear panel of the freezer, which sits directly against the refrigerant tubing.
- A screwdriver slipped against an evaporator tube causes a refrigerant leak, which turns a sensor job into sealed-system work.
- Using a heat gun or hair dryer to clear frost melts the liner and distorts the panel that holds the sensor.
- A defrost sensor refitted loosely reads the air rather than the coil, so the defrost cycle never ends at the right moment even with a new part.
Opening a panel to inspect or repair something yourself doesn't automatically cancel your manufacturer's warranty — but it can risk accidental damage, and some manufacturers do have specific service conditions. Check your product's warranty terms, or ask us, before deciding.