The low pressure alarm occurs when the suction pressure drops below the allowable limit.
Low heat transfer
A dirty external heat exchanger, restricted airflow, or low load can affect the evaporation pressure.
Refrigerant quantity
Insufficient charge or a refrigerant leak are possible causes, but should not be assumed without measurements.
Expansion valve
Incorrect control or a restriction in the electronic expansion valve can reduce refrigerant flow.
Proper diagnosis
Correlation of pressures, temperatures, superheat, and actual operating conditions is required.