Arrived on site to perform diagnostic on 5 year old Guardian unit. Homeowner states that upstairs unit is not cooling, is only blowing out room temperature air. Cycled system for cooling. Indoor and outdoor unit start up normally. System not producing temperature split at all. Gauged up to unit and found unit to be completely flat on refrigerant. Performed visual inspection of indoor and outdoor coil to try to locate leak but had no leak. Pressured lineset . Went into attic and can hear refrigerant leaking from the lineset but can not visually locate it do to location in the attic. System held pressure for about 10 minutes before going completely flat again. Leak needs to be repaired. Homeowner wants to hold off on repairs for now, as cooler temperatures are coming. No other work performed, system is not operational upon departure.