What was found
CREW REPORTED THE LEFT ENVIRO FAIL CAME ON AT 1000 FT AGL, SYSTEM WAS RECYCLED PER THE CHECKLIST, AND CAME ON AGAIN AT 5000 FT AGL. CREW RETURNED TO STATION. THE RIGHT ENVIRONMENTAL SYSTEM WAS PREVIOUSLY DEFERRED. LEFT SIDE OF OVERPRESSURE SWITCH CONNECTOR HAD A PIN IN THE CONNECTOR THAT WAS FOUND UNSEATED. RESEATED PIN. RIGHT SIDE DEFERRAL WAS CLEARED BY CLEANING & RESEATING CONNECTOR P563 TO THE OVERPRESSURE SWITCH. GROUND RUN OPERATIONAL & FUNCTION CHECK WERE GOOD. AN OPERATIONAL CHECK FLIGHT WAS COMPLETED, BOTH SYSTEMS OPS CHECK NORMALLY.