Fixed mine, turned out that the ecu was holding it back.
The ecu has a few states which it wil turn the ac off, most are safety related, but one of them is when you want full power out of your engine it will quickly switch the compressor off to minimise the draw.
I suspect when the nistune went in this was altered or something, mine was keeping that switch off. We rewired this so it listenes to the ac head unit not the ecu on that one. And bam Crispy cold air ready for summer