Manufacturer Lennox Model # 13ACXN036-230-17 Serial # 1915E29700 Completed a preventative maintenance on a Len unit. I was taking the split temperature and it was only 9 degrees. The system was low on 4-10a. I added a pound of refrigerant so I could properly perform the maintenance. Changed out 16x25x1 filter. Did a amp check on the condenser fan motor and compressor both are working properly at this point. After adding 1 pound of 4-10A system is operating properly at this time.