Came out to call for a system not cooling properly. Found that the unit had faulted out due to low pressure. Checked pressures and found the system completely out of refrigerant. Did a complimentary minor leak search on it and couldn’t find anything. We’ll be coming back Monday to do a complete leak search on system and discuss options based on findings. Came back out to do complete leak search on system. After checking the system over with a leak detector, I wasn’t able to trace down a leak at this time. I am unsure of how the system is out of refrigerant, as the unit held 200 psi for 15 minutes, and we were out to do the maintenance in June. Discussed with customer about other options. Customer was interested in doing the leak stop and charging the system. I cleared and charged system and added leak stop to it. I added 6.7lbs of 410a, and system is calling for around 8lbs. Told customer I’d come back and finish the charging it, and also double check the systems operation. Fi