Looking for a Central Unit compatable with a carrier down flow 58 RAV. The furnance is only 9 yrs but the ac has a slow leak. The inside coil looks very rusty. I had the leak checked and it was recharged one month ago, but didn't do anything about the leak. That was $130. Now they want to replace the AC for $2000 with a Reem. I have no idea what would be a good unit, but I really question Carriers' reliability .