I found this on the net -
Why does my car sputter when AC is on?
Low Refrigerant in the AC System: If your AC system is low on refrigerant, it will make the compressor cycle on more frequently, increasing the load on your engine. ... Bad Belt: One often overlooked cause of a car surging with the AC on is actually a worn compressor belt.
So hopefully not a major problem.
Titanium X Tectonic Silver 1.0 125ps Eco.