Adding to what Joe said - EPA can assess a fine of $37,500 for the intentional release of refrigerant. There is also a potential reward for reporters of this activity. A lot of contractors take the salvage value into account when bidding thier work. The refrigerant alone in that unit could be worth a significant amount of money, not to mention the coils, compressor, motor and copper. Most contractors would be willing to allow the owner to keep the unit, provided they either didn't want it or they knew about ahead of time. Personally, I wouldn't expect a contractor to believe a tenant about something like that. Yes, you can get them drained by professionals, but what is that going to cost you. My guess to have an hvac guy come to your house and do it is at least a 1 hour charge at 75 per hour. What is left after you pay that?