Upon my arrival I evaluated 1 straight cool furnace system. I verified system safety and performance is to manufacture specifications. Flushed and treated the water removal system. Cleaned the electrical cabinet and washed unit using water. Found the system is slightly low on refrigerant. Spoke with the customer over the phone and she approved to recalibrate the systems refrigerant today while on site. We added in 1lb of refrigerant to bring the system back to manufacture specifications.