I performed a singlee system cooling maintenance. I checked amps, capacitor, filter, electrical, drains, cleanliness, and refrigerant. I found that the primary drain was clogged in the p trap. I performed a drain clear with drain treatment and ensured that it was clear and free flowing. I found that the system was low on refrigerant charge. I did not notice any leak during service so I charge it with 4 pounds are 410a. The original delta was 10 degrees. The new delta is 19 degrees. The system is supplying 55 degree air. I collected for the drain clear and refrigerant. I will need to return with no rinse coil cleaner on Tuesday the 6th between 10-12.