When the Nexus controls your air conditioner, it can watch refrigerant pressure through an A/C pressure sensor. Maximum Pressure is the ceiling: if system pressure goes above this value, the ECU turns the compressor off to protect it and the rest of the system. High pressure usually means the condenser isn't shedding heat, from a failed fan, blocked fins or an overcharged system.
There's no universal number. The right value depends on your A/C system, so check the specifications for your compressor and refrigerant, and set the cutoff comfortably below any mechanical relief valve. You need this setting when the ECU controls the compressor clutch with a pressure sensor fitted. See air conditioner setup, A/C wiring and A/C pressure sensor configuration.
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