The compressor of our 1993 TETCO ES-3.5 geothermal furnace bit the dust 2 weeks ago. The options we are looking at are having an HVAC tech replace the compressor, paying an installer $12K+ to install a new 4 ton unit (our existing horizontal 6 pipe, closed loop system seems to be fine and is rated for 4 ton max), or install a new 4 ton unit myself for $6-7K. I am an avid DIYer who built our home (with a lot of help) and does most auto maintenance. I have also done some electrical and plumbing. As a teacher I have more time for this in the summer. I would love to read feedback from others regarding DIY installations. Once I found that the geo units came pre-charged with R-410a it seemed possible. It appears that a couple of suppliers ( TerraSource and Ingrams Water and Heat) cater to DIY installations and offer tech support. Our home is in Southwest Ohio. Thanks!!