Yes, you need to blow with compressed air. The A/C flush chemical "cleans" and degreases, and loosens the particles. But you can't get the particles out unless you blow them out at high velocity. Think about it - how will you remove a tiny speck of dirt from the middle of the evaporator coil without high velocity air?

The vacuuming process is not what you are thinking. It's not like using a vacuum cleaner. You'll be hooking the vac pump up to a sealed system. The function of vacuuming is removal of moisture, but it does absolutely nothing with solids or other dirt particles in the system.

Did your compressor fail? If so, it's even more imperative that you blow out with compressed air to remove any metal particles.

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280