Lennox Air Conditioner Error Code 11

Error code 11 on a Lennox air conditioner means the compressor temperature sensor wires have shorted together. The control board detected an abnormally low resistance in the sensor circuit, which falls outside any valid temperature reading range. The system flags this fault to prevent the compressor from running without reliable thermal protection.

You should not attempt to bypass or ignore error code 11. The compressor temperature sensor is a key protection component, and running the compressor without a functioning sensor circuit removes an important safeguard against thermal overload. Continued operation under this fault condition risks compressor damage, which is a significantly more costly repair than addressing the sensor wiring fault.

Resetting the unit by cycling power may temporarily clear the fault display, but the error code 11 will return as soon as the control board re-evaluates the sensor circuit and detects the short condition again. A reset does not address the underlying wiring fault. The short circuit in the sensor wiring must be physically located and corrected before the error will clear permanently.

A knowledgeable DIYer can perform a visual inspection of the sensor wiring for obvious damage, pinch points, or connector issues. However, working near the compressor and control board involves electrical hazards, and the system may contain refrigerant under pressure. If the wiring inspection does not reveal an obvious fault, it is advisable to have a qualified HVAC technician perform further diagnosis and any component replacement.

If the fault is limited to a damaged wire or connector, repair costs are typically in the range of $75 to $200 for a service call and wiring repair. If the compressor temperature sensor itself requires replacement, expect parts and labor to range from $150 to $400 depending on the model and technician rates in your area. A full harness replacement or control board involvement would push costs toward the higher end of that range.