Upon arrival tech was informed system #7 had a blank thermostat. Tech inspected system and found secondary drain pan full of water causing float switch to trip. Tech removed approximately 15 gallons of water from secondary drain pan. Took trap off system and cleaned with brush and blew nitrogen through trap and drain line. Poured water through drain and say it draining with no challenges. Thermostat came back on and system started up. System is back operational at this time.