Hi All, I have a 20 year old Lennox 5 ton system That was installed new for me. The compressor has given up the fight according to a repair man I had look at it. I am pretty up on this stuff and I believe it is true. It has been a good unit and we are happy with Lennox. My question is what are the developments in the newer units to make them have a high seer rating? I know on my pool equipment they have made dramatic improvements in the efficiency and assume this is the same. Do they have variable speeds or larger cooling fans on the compressor? Just interested in the reason for greater efficiency. Thank you for your thoughts. I hope I am asking the right area of this forum. Ken