A refrigeration system, comprising: a compressor to compress a refrigerant; a condenser disposed downstream of the compressor to condense the refrigerant; an evaporator disposed downstream of the condenser to vaporize the refrigerant; refrigerant lines (122-1 - 122-5) fluidly connecting the compressor, the condenser and the evaporator in series to form a refrigerant circuit for circulating the refrigerant; wherein the system further comprises: a receiver drier unit disposed between the condenser and the evaporator; and an accumulator unit disposed between the evaporator and the compressor, wherein the receiver drier unit comprises: a receiver drier configured to perform one or more of the following: temporarily store the refrigerant; and absorb moisture from the refrigerant; a first sensor installed at the receiver drier for measuring temperature and pressure of the refrigerant after it has passed through the condenser; wherein the accumulator unit comprises: an accumulator configured to restrict liquid refrigerant from entering the compressor; a second sensor installed at the accumulator for measuring temperature and pressure of the refrigerant after it has passed through the evaporator; and an electronic valve installed at the receiver drier or at the accumulator; the refrigeration system further comprising: a controller electrically connected to the electronic valve, the controller being configured to: determine a refrigerant sub-cooling level based on the temperature and pressure measured by the first sensor; and determine a refrigerant super-heating level based on the temperature and pressure measured by the second sensor; calculate a refrigerant charge level based at least in part on the determined sub-cooling level and the determined super-heating level; determine whether the refrigerant charge level is below a predetermined refrigerant charge level; and selectively control the electronic valve to allow flow of the refrigerant from a refrigerant reservoir fluidly connected to the electronic valve to the refrigerant circuit if it is determined that the refrigerant charge level is below the predetermined refrigerant charge level, thereby raising the refrigerant charge level to above the predetermined refrigerant charge level. a compressor to compress a refrigerant; a condenser disposed downstream of the compressor to condense the refrigerant; an evaporator disposed downstream of the condenser to vaporize the refrigerant; refrigerant lines (122-1 - 122-5) fluidly connecting the compressor, the condenser and the evaporator in series to form a refrigerant circuit for circulating the refrigerant; wherein the receiver drier unit comprises: a receiver drier configured to perform one or more of the following: temporarily store the refrigerant; and absorb moisture from the refrigerant; a first sensor installed at the receiver drier for measuring temperature and pressure of the refrigerant after it has passed through the condenser; temporarily store the refrigerant; and absorb moisture from the refrigerant; a first sensor installed at the receiver drier for measuring temperature and pressure of the refrigerant after it has passed through the condenser; wherein the accumulator unit comprises: an accumulator configured to restrict liquid refrigerant from entering the compressor; a second sensor installed at the accumulator for measuring temperature and pressure of the refrigerant after it has passed through the evaporator; and an electronic valve installed at the receiver drier or at the accumulator; an accumulator configured to restrict liquid refrigerant from entering the compressor; a second sensor installed at the accumulator for measuring temperature and pressure of the refrigerant after it has passed through the evaporator; and an electronic valve installed at the receiver drier or at the accumulator; the refrigeration system further comprising: a controller electrically connected to the electronic valve, the controller being configured to: determine a refrigerant sub-cooling level based on the temperature and pressure measured by the first sensor; and determine a refrigerant super-heating level based on the temperature and pressure measured by the second sensor; calculate a refrigerant charge level based at least in part on the determined sub-cooling level and the determined super-heating level; determine whether the refrigerant charge level is below a predetermined refrigerant charge level; and selectively control the electronic valve to allow flow of the refrigerant from a refrigerant reservoir fluidly connected to the electronic valve to the refrigerant circuit if it is determined that the refrigerant charge level is below the predetermined refrigerant charge level, thereby raising the refrigerant charge level to above the predetermined refrigerant charge level. determine a refrigerant sub-cooling level based on the temperature and pressure measured by the first sensor; and determine a refrigerant super-heating level based on the temperature and pressure measured by the second sensor; calculate a refrigerant charge level based at least in part on the determined sub-cooling level and the determined super-heating level; determine whether the refrigerant charge level is below a predetermined refrigerant charge level; and selectively control the electronic valve to allow flow of the refrigerant from a refrigerant reservoir fluidly connected to the electronic valve to the refrigerant circuit if it is determined that the refrigerant charge level is below the predetermined refrigerant charge level, thereby raising the refrigerant charge level to above the predetermined refrigerant charge level.