[rohrmann]

Even though the breakers appeared to have not tripped, if you haven't already done so, fully turn the breaker off that feeds the non working A/C, and then back on again. You also may want to verify that the 50 amp main did not trip on the leg that feeds that same A/C. Another possibility if all those things are good, is possibly the hot leg came loose from the breaker, or the wire nut connection came loose in the junction box at the A/C. Good luck.