Service diagnostic found that the condensation drain line was clogged. Water had backed up into the safety switch and shift down the system. I spoke to the homeowner about what I had found and presented options for repair. He chose to have the drain line cleared. I cleared the drain line and inspected the primary pan. I flow tested the drain with water and clear water was observed flowing out of the drain line. I then treated the drain line and function tested the system. The system ran without issues until it reached the set temperature on the thermostat. The system was running at the completion of service.