I had this same problem in Florida with an A/H in the garage. Do you have a variable speed A/H? See if the dip switches are set correct and make sure the installers didn't hook the yellow wires to YLo on the terminal board in the A/H. I would check the split like someone already suggested. I went to a call back where techs kept putting cork tape and insulation on everything. The Trane service rep told me to increase the cfm to 450 on the dip switches, check for return duct leaks, and to remove the horizontal pan inside the unit. I never got a call back on it, and the lady even told me to expect her to call if this doesn't solve the problem. I know Trane tells you to remove the horizontal pan on vertical applications with its cased coils, but I can't remember reading that about A/H. The guy told me that it is in the installer setup, but who reads the installer setups anyway.