1 system ac tune up complete. Installed union on drain line and cleared line. Tested mechanical and electrical components. Found weak blower capacitor (7.5uf).Found evaporator coil to be very rusty and corroded. Found main electrical switch to have electrical pitting present. Coil was starting to freeze because of low refrigerant pressure. Due to age and condition of system, recommend upgrading system to a more reliable, more efficient system. System is cooling at this time.