I have an ICF house with foam insulation in the attic. Installed a Trane XL16 5 ton 410a unit in Nov 2004. Summer 2005 expansion valve failed and compressor would not go into second stage. Both were replaced. Summer 2006, again compressor would not go into second stage. Compressor on order. I am quickly loosing confidence in this Trane system. Do I just have a lemon? Or is this a more wide spread problem? I have a variable speed air handler; can I upgrade to a XL19 and just replace the outside unit?