noquacks, think of the compressor in comparison to an internal combustion engine. They both have an intake and an exhaust...the refrigerant compressor's suction port is like the intake port on an engine. The same comparison can be made for the discharge port of the compressor, likening that to the engine's exhaust.
The only time there should be a true vacuum in the system is when a vacuum is pulled to remove air and moisture prior to adding refrigerant.
The only time there should be a true vacuum in the system is when a vacuum is pulled to remove air and moisture prior to adding refrigerant.