Oh Malabo. That isn't quite true is it. CHC had a Global policy of no aircon in any helicopters at that time if it was optional. A silly rule but there you go.
Payload was about as good as the 76 in the 139 even with the lower gross weight. The real difference was in the real world Nigeria DOC's, where the 139 was cheaper than a 76 because the C+ engines couldn't hack it and were changed out every 600-1000 hours. $$$.
31060, 31070 and 31072 all went to Nigeria without A/C. Yes, resourceful engineers put gasper vents in the windows but it was also resourceful engineers that painted out the glasshouse windows so that the pilots wouldn't put their maps up there for some shade. Pilots in NIgeria would never get their hands dirty with housepaint dear boy! Too busy racing home to the bar and the nightfighters.
If CHC were smarter they would have put the A/C in at the start an not saved the dollars. The weight of the old A/C system is about the same as one person with a bag.
The only thing the 139 couldn't do in Nigeria that the 76 always did do, was break the autopilot. The 139 just kept on trucking. LOL