Auto A/C Terms - Glossary
Low Side Service Valve - Charge Port

Typically the A/C system will include two charge ports or service valves. One each for the high and low side of the system. The low side service valve or charge port will be located between the evaporator outlet and the compressor inlet.

The high side charge port will be located anywhere between the compressor outlet to the expansion valve inlet.

The service ports provide access to the A/C system in order to check system pressures, add refrigerant or pull vacuum.

Older R-12 A/C system service ports were threaded male flare fittings that the service hoses threaded onto. Typically, the high side port was smaller than the low side port so that they were not confused.

On R-134a systems, the service ports are known as quick coupler ports. They require couplers that will snap onto the charge ports in order to access refrigerant pressures.

Understand that even though older R-12 manifold pressure gauge sets may include hoses with threaded ends for R-12 systems, they can be converted to work with R-134a by simply adding the proper adapters.