The air conditioning pressure sensor is generally installed after the dryer to detect the hydraulic pressure of liquid refrigerant flowing through the expansion valve. Three wires: detect high and low voltage. When there is fluorine leakage and compressor oil leakage after a car collision, in order to prevent damage to the compressor due to running out of oil, once low pressure is detected, quickly cut off the power supply to the compressor. When high pressure is detected, the compressor power needs to be reduced to avoid wasting work. In general, two are used for traditional fuel vehicles and four are used for new energy vehicles.