DURING PUSHBACK AT MIA MD80 STRIKES GND AIR CONDITIONING VEHICLE.

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GND CREW CHKED IN WITH CAPT WITH 'ALL READY TO GO.' THE CAPT CALLED FOR 'JUST PRIOR TO PUSH OUT CHKLIST.' AFTER CHKLIST WAS COMPLETE; CAPT CHKED BACK IN WITH THE GND CREW AND SAID 'PARKING BRAKES RELEASED WE'RE CALLING FOR PUSH.' I CALLED THE RAMP AND RECEIVED PUSH CLRNC. CAPT CHKED IN AGAIN WITH GND CREW WITH 'PARKING BRAKES RELEASED CLRED FOR PUSH.' PUSH WAS INITIATED; SHORTLY AFTER PUSH BEGAN WE ABRUPTLY CAME TO A STOP. DURING THE NEXT FEW MINS NO CONVERSATION TOOK PLACE BTWN THE TUG OPERATOR AND THE CAPT. THE ASSUMPTION WAS MADE BY US THAT THE TUG OR THE PLANE MADE CONTACT WITH SOMETHING. THE CAPT AND I OBSERVED THE GND CREW APCHING THE TUG OPERATOR AND SHAKING THEIR HEADS. AT THAT POINT WE ASSUMED CONTACT WAS MADE AND THE CAPT ASKED ME TO CALL THE RAMP AND TELL THEM WHAT WE THINK IS GONG ON AND CANCEL THE PUSH. APPROX 5 MINS HAD GONE BY WHEN THE GND CREW CHKED BACK IN WITH THE CAPT. THEY ASKED HIM TO SET THE PARKING BRAKE AND INFORMED US THE L WING CONTACTED AN AIR CONDITIONING CART DURING PUSH. THE NEXT CONVERSATION THE CAPT HAD WAS WITH MAINT. MAINT TOLD US THE L WING POS LIGHT WAS BROKEN AND THEY WERE WORKING ON A FIX. AS A NOTE I WOULD LIKE TO ALSO ADD A FEW OBSERVATIONS AS THE FO DURING THE ABOVE EVENT. ONCE I TOLD THE CAPT WE WERE CLRED TO PUSH I INSTINCTIVELY LOOKED OUT THE WINDOW AT THE TUG DRIVER. I OBSERVED HIM RELEASE THE TUG BRAKE AND THEN START THE PUSH. THEN HE LEANED OVER AND LOOKED TO THE R OF THE TUG TRYING TO MAKE SURE HE WOULD MISS HITTING A GND ELECTRIC CART. HE EVEN SLIGHTLY TURNED THE WHEEL OF THE TUG TO MISS THE CART WHICH WAS INCHES AWAY. I WOULD SAY WE MOVED ABOUT 2 FT WHEN HE LOOKED UP TOWARDS THE RAMP AND THEN WE ABRUPTLY STOPPED. I THEN SAW HIM BOW HIS HEAD AS THE OTHER RAMP WORKERS CAME UP WITH THEIR ARMS OUT AS TO GESTURE WHAT ARE YOU DOING. AT THAT POINT THE TUG DRIVER GOT OUT AND THEY ALL MOVED TO THE L SIDE OF THE ACFT OUT OF MY VIEW.