Releasing pressurized gas absorbs heat so simply running the released gas through a set of A/C coils would provide indirect A/C or you could merely vent the "exhaust" (it is air, after all) into the passenger compartment since that "exhaust" should be very cold.
Releasing pressurized gas is cold when there is a phase change, i.e. from liquid to gas. Going from high pressure gas to low does involve a temperature drop but it's not going to be anything like a real air conditioner.
Have you ever fired a PCP(pre-charged pneumatic) air gun? No phase change; much icing. Yes, the latent heat of phase change makes an enormous difference, but it doesn't mean that the pressure drop alone won't cause a big enough temperature differential, and since you're not in a closed compression/decompression loop, you wouldn't be particularly worried about the efficiency -- you're just using a byproduct of the propulsion system that would otherwise be wasted.
It's a cute answer, but very inefficient. You're throwing away the mechanical energy. Also bear in mind that "refueling" with compressed air will heat up your car.
In fact, if the air conditioner coils are between the air tank and the engine, the air conditioner could make it more efficient, if you don't have some other kind of regenerator-in-a-dewar trick going on.
Releasing pressurized gas absorbs heat so simply running the released gas through a set of A/C coils would provide indirect A/C or you could merely vent the "exhaust" (it is air, after all) into the passenger compartment since that "exhaust" should be very cold.