2016 3t Lennox hp attic horizontal. Homeowner was not home upon arrival, waited appropriately. Recieved permission from homeowner through dispatch to look at the condenser unit. System off upon arrival. Once homeowner arrived. I accessed the indoor unit and quickly found the SAFTEY drain switch had been activated on the secondary line. I cleared the drain blockage, monitored refrigerant system. Fully functional and cooling upon departure. I expressed concerns about maintenance but homeowner declined membership. Homeowner also claimed the system hasn't been on for a month. Homeowner purchased a drain clear.