Do not use the blow out method in a Hydro/AquaHot equipped motorhome. The risk is that, no matter what source of compressed air you use, there may not be enough volume and pressure to completely clear the fresh water coils. If some remains it will drain and collect in the bottom of the coils. If it then freezes, the repair price will take your breath away.
You can use compressed air for the rest of the system, but after the blow out, you need to run RV antifreeze through the HydroHot. And, if you have a Splendide, you can't blow that out either.