Samsung Air Conditioner Error Code E291

Samsung air conditioner error code E291 indicates a fault in the high pressure sensor circuit. The high pressure sensor monitors refrigerant pressure on the discharge side of the compressor, and the control board uses its voltage signal to protect the system from dangerous over-pressure conditions. The E291 code is triggered when the sensor output voltage falls outside the expected operating range: a short circuit condition is detected when the signal drops below 0.4V, and an open circuit condition is detected when the signal rises above 4.2V. Both conditions tell the control board that it is receiving an invalid reading and cannot reliably monitor system pressure.

The most likely causes are wiring failures or sensor component failure. A broken wire, loose connector, or corroded terminal in the sensor harness can interrupt the signal path and drive the voltage outside the valid range. The sensor itself can also fail internally, producing an out-of-range output even when wiring is intact. Because the high pressure sensor plays a direct role in protecting the compressor from over-pressure damage, the system will typically suspend normal operation when this error is active.

Diagnosis should begin with a careful inspection of the sensor wiring harness for any visible breaks, pinching, corrosion, or loose connector pins. After confirming wiring integrity, the sensor output voltage should be checked at the control board connector with the unit powered. A reading below 0.4V points to a short in the circuit, while a reading above 4.2V points to an open circuit. If wiring checks out, the sensor itself is likely faulty and should be replaced.