The power draw of the A/C unit had nothing to do with the fact that no other cars got A/C.
Despite the fact that the roof of the CLRV is designed to handle a pantograph, it's only designed to do so in one place - where the pole is currently mounted. The roof forward of that point isn't designed for that kind of weight, so 4041 had to have its roof strengthened to handle it.
As well, they needed to run new power wires from the LVPS and main breaker underneath the car back up through the sides of the car to the roof. It wasn't an impossible task, but it was just another headache that needed to be done to make it work.
Finally, the whole idea of refitting the cars with A/C was paired up with the project to thoroughly rebuild a bunch of cars for another 15 years of service. This would have also included replacing and upgrading the propulsion control systems as well. Alas, this was nixed shortly after the contract for the Flexities was signed. And so no other cars were retrofitted save for the one which was done as a test.
Dan