My unit that we installed new in 2008 finally could not keep up with the 100 degree heat we had this week. Had me worried. I called my favorite HVAC dude and he put 3 pounds in it. Kinda sucks because it shouldn't leak at all. He told me Lennox has a class action suit for slow leaking systems. I'll be happy if I can get a few more years out of it with just charging it every now and then. You HVAC guys: Am I crazy for thinking that?