Came out to call. Customer said AC wasn’t cooling properly. He changed the filter and tried washing the unit. He thinks it’s low on refrigerant. I checked the system over and found it to be low on refrigerant. I was actually able to find oil residue on the elbow of the suction line going into the evaporator coil. I made homeowner aware of the potential leak in the system. Went over some options with him to repair it. Customer chose to just add refrigerant at this time. He approved 2lbs of 410a. I added 2.1lbs of refrigerant to system. System still needs a little more refrigerant for it to be operating efficiently. He wants to wait for now.