Pressure switch
The pressure switch is in the air conditioning has one or several functions, depending on the vehicle manufacturer.
The low pressure switch has the function of shutting off the air conditioning at low pressure in the air conditioning, and the high pressure switch assumes the function of the closure to protect the compressor and the plant if too much pressure that builds up in the air-conditioning, usually at 20 BAR pressure.
There are also pressure switches installed with multiple function, eg The binary pressure switch the function of shutting off the air conditioning is too low (0.5 - 1.5 bar) or high pressure (20 bar) to make.
The Trinary pressure switch has the function of the binary pressure switch, plus the function of the sharing of the fan for the condenser at 16 Bar.

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