As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON TAXI OUT THE ODOR OF BURNING EMANATED FROM THE AIR CONDITIONING PACKS. WE SHUTDOWN THE RT PACK AND THE BURNING ODOR DID NOT ABATE BUT CONTINUED WITH THE LT PACK, ONLY OPERATING. RAN ENGINES AND PACKS TOGETHER AND ISOLATED FOR SEVERAL MINUTES. COULD NOT DUPLICATE ODOR. FOUND LT RUNWAY T/O LIGHT SWITCH ARCING AND MELTED. REPLACED SWITCH IAW SWPM 20-83-11. OPS CHECK GOOD.