The expansion valve opens when there is enough pressure in the system and then it fills the evaporator in the vehicle blows cold air returns to the condensor in front of the radiator in the form of liquid gets cooled is repressurized by the compressor expansion valve opens along with the high and low pressure switches and the process keeps repeating itself.So in order for the system to operate correctly all components must be checked and eplaced accordingly and most importantly the system must be fully charged! Oh by the way, the expansion valve should be located on the firewall in the center of the vehicle just follow the lines from the compressor,to an aluminum block.

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