Customer has part and labor warranty. On arrival found system in a low pressure lockout. Refrigerant level was slightly low. Today technician added 2 pounds of 410a refrigerant. Inspected systems, compressor, fan motor and air handler blower motor. Performed electronic leak search, but did not pick up any leaking refrigerant or signs of leaks at the indoor or the outdoor units. Did notice that one of the service caps was missing and if unit had recently been maintenance it’s possible that Schrader was leaking.. Made sure service caps were secured. System is operating normally at this time.