Performed cooling maintenance on one straight cool system. Checked all electrical, mechanical and performance of the system. Cleared and treated the drain line and washed the outdoor coil. I found that the system is slightly low on refrigerant. I spoke to the customer, and he chose to have refrigerant added today. I added 14 ounces of refrigerant and performed a leak check on the system. I was not able to find a leak on the system. No other major issues were found, and the system is operational at this time.