I have an 05 Expedition with 5.4. The motor was shuddering and throwing a code P0306. What I did to fix the problem was to replace the spark plug on #6 cylinder with a new Motorcraft SP515. During this replacement I noticed that the connector for the fuel injector for that cylinder was a little bit dirty. The original spark plug that I removed actually looked in very good shape. The motor has 125,000 miles on it. Plugs had never been changed. After removal and replacement of plug I cleared the code with my OBD II scan tool. This solved the shuddering and no codes have come back again. The only problem is immediately upon solving this problem, my AC quit working. It wasn't a slow fizzle, it just immediately died after I reset with my scan tool. The AC has never given me any problems in the past, not like it had low refridgerant. It went from ice cold to dead after resetting the code. I have checked fuses #11 #13 #18 in side kick panel. Did not replace them, but visually the fuses look good. I know in the engine compartment there is aux fuse panel with a clutch relay in it and also a diode. Have not checked those, but really don't have the tool to see if those are bad or not without putting in new replacements to see what happens. Haven't found anything on the forum talking about if there is a master reset for the AC system, something that I'm missing, but doing some Google searches I have seen that people have had problems with their AC conking out after removing the coil on one of their spark plugs for a spark plug removal. Is this something that happens, or is it a freak incident? Any help in this matter is much appreciated.