On arrival secondary drain line float switch was tripped. Removed p trap at sink and blew down HVAC line. Hooked shop vac back up at unit and it pulled a strong vacuum through HVAC line. Primed p trap and system resumed cooling. Advised customer that the drain line is definitely clear, but if this problem persists we will either need to add a sump pump to the system or have a plumber give quote on rebuilding drain line that is passing through drywall. Plumber visit needs to be scheduled for Tuesday