Plugs have nothing to do with a/c, although you need to take care of the misfire. If you let it go a long time you run the risk of ruining your catalytic converter (causing code P0420) and that could be big money. Your code right now is probably P0300 (random misfire) or any one or more of P0301 – P0306, 301 being 1 cylinder misfire, 302 = 2nd cylinder misfire and so on. Your ac is probably leaking from the valves. Get a can of r134a that comes with a dye and charge it and shine an ultraviolet flashlight on the lines specifically where the lines connect to the condenser and receiver dryer , basically where the pipe meets another part. you can get an ultraviolet flashlight for cheap from amazon, the kit comes with yellow plastic glasses. they make the dye glow when you shine the light where it leaks.