The first piece of equipment I bought when doing these types of minisplits was buy the shrader adapters--can not work on the R-410a systems without them. Sounds like you've been had. Cut your losses and get the first contractor, or another reputable contractor, out to get the system repaired correctly. It may cost you more now, but it will be done properly. Everything this guy did seems very wrong, especially blowing the charge out of the system. I would have told him to leave right then and there--if he gave me trouble, the police would have been there to escort him away.
Hey, isn't there a reward for reporting EPA violations?
Maybe that will cover having a pro clean up this what this hack did.
I am holding study groups at work for the 608 and 609 certifications and just went over this. The EPA can assess a fine up to $32,500 per violation, per occurance - this "hack" would be toast were he reported. The EPA can also award up to $10,000 as a reward for turning someone in.