Front air cond. won't turn on.

The outside unit may have a stuck cooler fan shaft. That can be overcome by pushing the fan blades that will rotate the shaft so it frees up. Do that before turning on unit. I use a wooden dowel about the size of your little finger in diameter and about three feet long, as it fits through the slotted openings in the sides so you don't have to take shroud off. The compressor won't start until fan outside is rotating, as it cools condenser on one end and blows air over the cooling coil and into the RV on the other end. The shaft gets rusted in place due to age and lack of use.