The geothermal unit in my house is dead for lack of a better term. It is an 22 year old Waterfurnace 5 ton R22 unit with a leaking coil. Rather than fix it, I feel it is time for a replacement. I replaced the ECM fan motor last year and the compressor is obsolete. I am getting quotes for different units now going from 10-17k depending on quality on the unit. I happened to stumble on a Climatemaster Triology 45 unit that is almost exactly what I need for 10-20% of the cost of an installed unit. The unit was in a house being built and someone tried to steal it until they realized how heavy it was, the insurance company totaled out the unit because it was moved and now the fellow has to dispose if it. He stated there are only minor scratches to the unit with no other damage. The unit seems to meet me specs, 5 ton, right hand return, internal flow center, 20kw resistance heat. So my question. Is a DIY self install of a geothermal system doable/practical? To me it doesn't look too complex. Disconnect power lines, disconnect the loop lines, disconnect the desuperheater, disconnect the return and supply vents, remove the old unit and reinstall the new one. The three areas I am unsure about is 1) how to adapt from the old flow center to internal Climate master unit. Basically how do you adapt HDPE pipe and put an extension to the i/o of the inti itself. Is there a barbed compression fitting or similar that I can use instead of need a HDPE fuser? 2) I don't have the tools (flush carts) to purge/flush the coolant in the loop.Short of spending 2k on a fluch cart are there any ways for a homeowner to overcome this hurdle? 3) once installed how I don't have the tools to knowledge to flow balance the unit. Am I just dreaming too big that a homeowner could do a DYI replacement of a a geothermal unit themselves? I am almost certain I would not be supported with warranty service or parts form Climatemaster, however if I get the unit for 10-20% and spend another 10-20% on parts/help, I could walk away with a 60-80% savings. This all is a gamble. Thoughts?

What area are you from? Local geo dealer may flush for you.

DIY? Sure, if you can read and follow the instructions in the Installation and Operation Manual (IOM).

You can use Geo-Stab fittings to transition from HDPE pipe to connect to the end of your loop header pipe then whatever threaded or barbed fittings necessary to connect to your geothermal unit. There are several suppliers of these fittings on the internet. Just search for [geo-stab] or [geothermal fittings] or [geothermal supplies]. You can find this stuff on ebay as well.

The Geo-Stab fittings are a little expensive, but a proven design and avoid the need to buy a lot of other tools and/or pay someone else to come in and fuse the pipe.

Here is one example: https://www.hdpesupply.com/1-1-4-ips-sdr11-geostab-x-1-male-brass-threaded-transition-mpt/

As far as flushing your loops, you don't have to have an expensive pre-made flush cart for a single DIY job. You can build what you need for <$300 using a 1-1/2 HP lawn sprinker pump (~$250 or less if you find one on ebay) mounted on a board attached to the top of a used 55 gallon food grade plastic barrel (~$15 at flea markets, junk stores, etc), and ~$35 worth of fittings and valves. You might even be able to rent a comparable water transfer pump rather than buy one.

New ebay 1-1/2 HP booster pump $136: http://www.ebay.com/itm/NEW-IN-BOX-Everbilt-EFLS15-HD-1-1-2-HP-4-020-GPH-Sprinkler-Pump/112332756076?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D2%26asc%3D41375%26meid%3Daf36db5f65a7456e80018cfb1fe3677f%26pid%3D100005%26rk%3D2%26rkt%3D6%26sd%3D332214151991

What do you mean "flow balance the unit"? The loop water flow pretty much takes care of itself if you get all of the air out of the lines. The fan blower speed is adjustable via switches. Just start with the default settings and adjust up or down based on comfort using the unit operating manual.

I'm not sure about the Trilogy 45 units, but the Climatemaster Tranquility 30 units have flushing "T"s and valves built into the front of the unit which makes it relatively simple to connect and flush the loop.

Edit:  I just looked up the Trilogy 45 manual - see link below.  It has the same flush ports and valves as the Tranquility 30.

http://www.climatemaster.com/geothermal-dealer/wp-content/uploads/2016/02/97b0112n01-climatemaster-residential-trilogy-45-q-mode-qe-series-horizontal-vertical-and-downflow-packaged-geothermal-heating-and-cooling-system-installation-manual.pdf