Where is the AC low pressure valve on a 1994 GMC Sierra?

On a 1994 GMC Sierra, the AC low pressure valve is typically located on the suction line, which runs between the evaporator and the compressor. It is usually found near the firewall on the passenger side of the engine bay. The valve is a small, threaded fitting that can be identified by its larger diameter compared to the high pressure valve. Always ensure the system is off and properly depressurized before attempting any service.