Frigidaire Refrigerator Error Code OP (FZ)

The OP (FZ) error code on a Frigidaire refrigerator indicates that the control board has detected an open circuit condition in the freezer thermistor. The freezer thermistor is a temperature-sensing resistor that continuously reports freezer compartment temperature data to the main control board. When the board reads a resistance value that falls outside the expected range, typically due to a broken circuit in the thermistor or its wiring, it logs this fault and displays OP (FZ) to alert the technician that valid temperature data is not being received from the freezer sensor.

Before replacing the thermistor itself, the wiring harness connecting the sensor to the control board must be inspected carefully. Pin back-outs at the connector, where a terminal has partially or fully backed out of its housing, are a frequent cause of this code and can mimic a failed thermistor. Similarly, pinched wires routed behind drawers or along the freezer liner can develop shorts or breaks over time. These wiring issues are often overlooked but should always be ruled out first, as they require no parts replacement.

If the wiring and connectors check out correctly, the thermistor itself is likely faulty. A thermistor in an open-circuit state will typically read infinite or very high resistance rather than the normal value expected at a given temperature. Testing the thermistor with a multimeter and comparing the reading to the expected resistance at the current freezer temperature will confirm whether the sensor has failed and needs to be replaced.