A refrigeration system comprising: a refrigerant evaporator coil (4a; 4b), vapor/liquid separation structure connected to an outlet of said evaporator coil via a refrigerant line configured to separate low pressure refrigerant vapor from low pressure refrigerant liquid; a refrigerant compressor connected to an outlet of said liquid-vapor separation device via the refrigerant line and configured to compress refrigerant vapor from said vapor liquid separation structure; a compressor discharge motorized valve connected to an outlet of said refrigerant compressor via the refrigerant line and configured for coarse regulation of discharge pressure during system start-up; a bypass pressure regulator valve connected to an outlet of said refrigerant compressor via the refrigerant line and configured for precise regulation of discharge pressure during start-up; an air-cooled refrigerant condenser comprising a plurality of condenser coils connected to said compressor discharge motorized valve and said bypass pressure regulator valve via the refrigerant line and configured to condense refrigerant vapor produced in said compressor to refrigerant liquid, a motorized valve (101; 102; 103) connected to an inlet of at least one of said condenser coils configured to provide control of gas feed to the condenser coil to allow pressure to build without collapsing oil pressure; a vertically oriented inline check valve (106; 107; 108; 109) connected to an outlet of at least one of said condenser coils configured to prevent liquid backflow; a collection vessel connected to an outlet of said condenser via refrigerant line for receiving refrigerant liquid from said condenser; the refrigerant line connecting an outlet of said collection vessel to an inlet of said vapor/liquid separation structure and configured to deliver refrigerant liquid to said separation structure; said vapor/liquid separation structure having a liquid outlet that is connected via the refrigerant line to an inlet of said evaporator coil; a pre-packaged modular enclosure; and wherein said vapor/liquid separation structure, said compressor, and said collection vessel, are situated inside the pre-packaged modular enclosure. a refrigerant evaporator coil (4a; 4b), vapor/liquid separation structure connected to an outlet of said evaporator coil via a refrigerant line configured to separate low pressure refrigerant vapor from low pressure refrigerant liquid; a refrigerant compressor connected to an outlet of said liquid-vapor separation device via the refrigerant line and configured to compress refrigerant vapor from said vapor liquid separation structure; a compressor discharge motorized valve connected to an outlet of said refrigerant compressor via the refrigerant line and configured for coarse regulation of discharge pressure during system start-up; a bypass pressure regulator valve connected to an outlet of said refrigerant compressor via the refrigerant line and configured for precise regulation of discharge pressure during start-up; an air-cooled refrigerant condenser comprising a plurality of condenser coils connected to said compressor discharge motorized valve and said bypass pressure regulator valve via the refrigerant line and configured to condense refrigerant vapor produced in said compressor to refrigerant liquid, a motorized valve (101; 102; 103) connected to an inlet of at least one of said condenser coils configured to provide control of gas feed to the condenser coil to allow pressure to build without collapsing oil pressure; a vertically oriented inline check valve (106; 107; 108; 109) connected to an outlet of at least one of said condenser coils configured to prevent liquid backflow; a collection vessel connected to an outlet of said condenser via refrigerant line for receiving refrigerant liquid from said condenser; the refrigerant line connecting an outlet of said collection vessel to an inlet of said vapor/liquid separation structure and configured to deliver refrigerant liquid to said separation structure; said vapor/liquid separation structure having a liquid outlet that is connected via the refrigerant line to an inlet of said evaporator coil; a pre-packaged modular enclosure; and wherein said vapor/liquid separation structure, said compressor, and said collection vessel, are situated inside the pre-packaged modular enclosure.