AC just wont keep cool

Took 96 in to get recharged, all was good for about 2-3 weeks. Took it back in, and something was tightened, freon added, all good for about a week. Back in, and $85 for a hose to be replaced. All good for a few days. Back in, and finally told the evaporator had a leak. Got that replaced (at no charge-because he felt bad that this has been ongoing problem). Did he feel bad, or did he not fix? Cuz AC ran cold for a few hours only. So if recharging, tightening, and replacing Hose, and Evaporator do not solve the problem. What other troubleshooting would there be? Any suggestions? (other than dump the mechanic)

bad compressor? freon a/c's are garbage now cuz in canada anyways you cannot purchase freon...i would have thought youd have a cfc free model and not freon...