First 139 to Nigeria didn't have air-con because customers wanted payload priority and the original gross weight meant it carried less than a 76 even before the air-con. Resourceful engineers cut gasper vents into the cabin windows, resourceful pilots painted out the skylights with house paint. The next ones had air-con. In the sun it is a lot hotter in a 139 than a 412/76. Hope the RAAF bean-counters didn't think of a/c as a luxury.