Depending on the fabricc of the awning will stipulate how is best to clean it. Under "normal" circumstances I would pressure wash it the same as the last cleaner did. However you can not always clean off algae, in most cases it has to be killed off. There is no reason unless damaged that awnings shuldnt clean up very well.
With all the new awnings going up due to the no smoking ban there should be lots of them to do.
Best, Dave.