Outside unit cycles but won't stay running. Causes low pressure line freeze up.

If the airflow through the indoor coil is as it should be (filter, coil, & fan all clean, registers all open & not blocked, ducts in good shape). Most likely the cause of the freezing is the refrigerant charge being low. Adding refrigerant requires a contractor licenened by EPA to handle refrigerants. If the system is low, the contractor should look for & repair the leak.