Air filters were replaced mid September and mid October by the customer. Air coils are clean. I pressurized the 2 ground loops to 65psi. I checked the electrical wiring and electrical systems, including the auxiliary heat strips and their safety devices, all are within specification. I operated the units on second stage heating mode and recorded 25-30 degrees temperature rise across the air coils except for unit #3, which was >30. I increased the blower speed to drop the temp rise to under 30. I calculated heat of extraction and they are all extracting slightly more heat from the loop than the printed data, which is great. Units are all operating normal. There is no surge protector on any of the equipment. Installing one on the main entrance panel will protect everything served by that panel. Also unit #3 in the attic may benefit from a Blue Tube ultra violet light and Ez Trap drain line assembly with built in overflow protector.