Performed customer spring home care maintenance visit 2 units Changed qty 2 (20x25x4) system filters Both systems are 3 years old. Checked over all operations of system for upstairs system. Customer showed me an error message that occurred over weekend that unit stated refrigerant low pressure lockout. Stated that system came back on Sunday and has been running ever since. Checked equipment and could not find any issues as to why this happened, refrigerant pressures were good, split temperatures showed good, system ran for an hour while I was here and did show and signs of error. Blower wheel is clean inside the cabinet is clean. Outdoor unit inverter board did not show any active error codes, condenser coils are clean. Advised customer that drain line is not draining properly and backing up. The line goes through chase of wall and then meets a tee in crawl space with other units drain. There are several bellies in the line causing water to hold still. Customer approved to have drain r