Jeremy, $4000 to recharge your A/C is a ridiculous price. Last year my basement unit was not cooling on the secondary system, so I took the unit out in about 2 hours by myself and took it to SCS, who was still in business at the time. They replaced a leaking line and recharged the unit for $200, and I reinstalled the unit. Total repairs, $210 (SCS service, silicone calking,and duck tape) and 3 hours labor (N/C on labor).
Any competent home A/C repair service can fix the unit unless you have a circuit board problem. The unit uses R-22 refrigerant an operates just like a mobile home A/C unit except it has 2 compressors. So it operates like two A/C units that are built together in one housing, and controlled by a special thermostat and circuit board.
The unit will have to be removed to check it for leaks and to recharge it. The unit is not that hard to remove. After removing my unit once, and learning how, I could remove and replace the unit in 2 to 3 hours working alone.
If you have anyone remove the unit, be sure that they repair the leak, and not just recharge it, because you will have to remove it again to recharge it again when that refrigerant leaks out, and it will.
Gerald