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Air Conditioner Pressure switch and sensor: What It Does and Signs It's Failing

Safety and control devices on the refrigerant lines in the outdoor unit. A high-pressure switch stops the compressor if pressure climbs too far, some systems add a low-pressure switch, and a pressure sensor gives the board a running reading.

How it works

The switch opens a circuit at a set pressure, and the board shuts the compressor down and shows a code. Sensors send a varying signal the board uses to control the system.

Signs it is failing

• The outdoor unit shuts down during hot afternoons
• High or low pressure codes
• Unit restarts and trips again soon after

High-pressure codes are most often caused by a dirty outdoor coil, blocked airflow or overcharging. GREE says to check coils and fans before suspecting the switch, and Daikin lists a dirty outdoor coil among the causes.

Can you replace it yourself?

Clean the outdoor coil, clear the area around the unit, then reset power; Fujitsu says to wait 3 to 5 minutes before switching back on. Never bypass or jumper a pressure switch. These parts sit on refrigerant fittings, so replacing one is work on the refrigerant circuit, which in the US is reserved for an EPA Section 608-certified technician.

Buying the right part

Leave it to the tech, who'll match the pressure rating to your model.

Error codes linked to the pressure switch and sensor

• A5Low pressure errorFujitsu
• E1High pressure protectionGree
• U1 / UdHigh pressure or overheat protectionMitsubishi Electric

Last reviewed 2026-10-19.