I agree with vreihen. First, to file a class action law suit you need a large group of people who have had the same issue, and second, the only people who get anything but satisfaction out of a class action law suit are the lawyers. I'd sue the Dealer for damages. The dealer either misdiagnosed the issue, and though paid to do so, failed to make timely repairs, resulting in the damage, or they incorrectly overcharged the system or failed to add the correct freon/oil mixture to the system, resulting in the damage, or a combination of both. Check your repair bills. Do they say the repair work is warrantied for any period of time? Even if not stated on the bill, a court will likely rule that is implied. Consult an attorney, and get an idea of what this will cost you (too large an amount for small claims court) in both money and time, and determine if you want to proceed - would seem to be a pretty strong case for negligence. The Dealer may look at the cost to defend against the claim in court, and decide to fold and negotiate a settlement well before it ever gets that far. Also, you should file a complaint with the Better Business Bureau. In some areas they have quite a bit of clout.
All said, if you determine the cost to pursue the Dealer is too much, or won't be effective, if it were my car, I think I'd weigh the chance and cost of taking it to an independent AC shop, along with printouts or links from the BMW service manual for the system, and the specs for pressurizing the system, and the special freon/oil mix it takes, have them flush the system, put in that debris screen that is supposed to protect the compressor, and see if that allows a few more years of life from the car, before just dumping it for salvage.
2015 i3 Rex, Capparis White, Tera World, Technology & Driving Assistant, Parking Assistant, Harman Kardon Audio System, 19 inch 427 wheels, EVoInnovate EVSE