My home is 9 years old. The GEO unit over the years has been having more and more problems cooling the 2nd story. The house has 4 zones. It freezes us out of other zones trying to reduce the temp in the upstairs zone. I have adjusted temp ranges to put most of the overflow cooling into the basement. (the least used part of the house) It does fine heating, it's only the cooling. Any suggestions on what my problem might be?