I am a commercial hvac tech, and decided to have a Carrier water source heat pump installed at my home in Lexington SC for its economies and because my well water is exceptially pure. I talked things over with Scott and Ryan Burnett owners of Air Core, commercial contractors locally and together we chose the Carrier Model 50YDH026PCK301 Model 026 18,000 - 24,000 btu, and orderred it with bells and whistles: I wanted the desuperheater; the corrosion resistant cupra-nickel coils, (because pure water tends towards the acidic side of the ph scale) the variable capacity Copeland Scroll, and the ecm energy saving motor. Right after the old furnace was pulled out, I hired Stanley Steamer to clean the ductwork. (We had a special needs daughter in our home) The returns in particular had 3/4" of dust and crap in them. The unit is suspended from vibration mounts. from under my house. I decided one year after the install in 2008, to add a Whirlpool wholehouse water filter which I installed outside my brickwall, because I sure wasn't going to crawl under my house to change the filter. inlet water temperature in the summer is 70 degrees. Lowest winter temperature I have measured is 58 degrees. Compressor amp draw at partial loading 5.8 amps. Well draws 8 amps and cycles on and off with air bladder tanks. at 230 volts. The 1/2 hp well apparantly can handle the load, though I am considerring putting in a 3/4 hp when this well goes 'south.' Full load compressor draw is 7.5 - 8 amps heating or cooling. I am also using the Honeywell Pro 8000 programable thermostat which I basically like but has acted quirky from time to time. In my opinion, do not use a stat less capable than this. I actually used it originally with my cast iron furnace. It is very flexible. Comments the biggest problems I have had have been with the original orange TACO valves. the first two stopped closing completely at the 14 -16 month range. After going through my second TACO valve ($180.00), I bought an Hunter 24 volt irrigation valve for $19.00 and installed it on the second stage. It works. At the moment, I am still using the original TACO on stage one, because it proves water flow before starting the compressor, and is slow opening, closing. I may replace number one with an equivalent Belimo, later. Problems: first one was that it would not generate any heat whatever. The problem was that the taco circulating pump would not come on because the klixon discharge temperature switch on compressor outlet is rated to come on at about 137 - 143 degrees F and this unit with R410a is so efficient that the line ran 116 - 132 most of the time. Originally I disconnected the klixon switch and straignt wired it to normally closed contacts on a 120 volt wireless controlled general purpose relay. I reduced water flow and then had all the hot water I wanted all summer long. At startup when we opened the water lines, water blew through an incompletely brazed joint at the taco pump. That was after all the signed quality assurance paperwork they sent with the heat pump. Ryan quickly rebrazed and corrected the poor braze on that water line. We are just starting winter, so I unwired the part of the taco pump that went through normally closed contacts on that relay. These were the contacts that allowed the circulating pump to run when the compressor started, and now the taco will only come on or off using my wireless remote control. My understanding is that ClimateMaster, the company who builds this Carrier model, has a new electronic board to solve the problem. I am currently checking with Carrier to see if they will furnish the board as a retrofit, since the desuper heater never worked from the factory. We'll see. The other problem I had was lockouts last winter. I had thought that suction pressure was going too low, but after carefully reading the code # 4 error out of the circuit board, it indicated low water coil temperature. I talked with RL at Climate Master who told me to strap a digital thermometer at the spot where the sensor was mounted. That sensor shuts off the compressor if it reads 30 degrees refrigerant going into the water coil. On test runs I found that the sensor was shutting the compressor off at 34 and 37 degrees. BINGO! Since Scott and Ryan are the "official licensed installers" they are checking on the sensor. My understanding at this point is that the compressor is warranted 10 years, all other parts, 5 Here are some changes I will be making. I will be purchasing the GE Hybrid hot water heater, installing it in my house, (no garage) and turning the present Whirlpool 50 gallon hot water heater into a preheater only without electricity. I will be running a second taco circulating pump to circulate hot water lines from the GE to my bathroom and the kitchen. By the way, never pull the factory refrigerant caps off of your heat pump unless you have trouble shot other things first, or evidence points to a leak in the system. This is year two. I'll post updates in the future. December 21, 2010 update I had had a lot of cold weather lock outs in 2009 / 2010 Error # 4 (coil temperature too low) I finally placed a Cooper temperature probe on the spot where the grey thermistor measures thermostatic expansion valve temperature just before the refrigerant is metered into the water coil. I found temperatures that dropped below 30 F; 23F , 17F, which is below the 30 degree trip point that locks out the compressor. I also found that the original freeze protection fp1 sensor (grey wires) false indicated two times at 37 F and 34 F. That grey sensor has been replaced. I wound up buying a bottle of R-410A (I do commercial hvac) and borrowing a weight scale from Ryan and Scott Burnett, the "official" installers of my heat pump. I hooked up a brand new set of German made Testo digital electronic gauges and the temperature sensor probes that come with the gauge set to measure subcooling and superheat. I could not measure ANY superheat or subcooling. At that point I realized I had a leak "somewhere" unless the plastic valve caps leaked. This model takes 58 oz of measured or "weighed in"charge from the factory. I MEASURED in 13 oz of 'borrowed R410A" the first night and suction and high side pressures started coming up along with heating capacity. That 17 degree measured temperature on the thermostatic expansion valve immediately came up in the 40's F, but then again dropped, until the charge was brought up to the the factory amount the following night. The following night I weighed in an additional 3 oz. Suction came up @ 130 psig; head pressure eventually @ 335 psig. Temperaure of liquid at the expansion valve stayed in the 40's, F. Heating capacity has returned to normal for now. While I don't have the exact Carrier pdf guideline pressures or subcooling, superheat values in front of me, you are generally looking for 5-15 degrees subcooling and something like that in superheat. ( If you have 2-3 degrees subcooling, you are undercharged; if you have 20 - 30 degrees subcooling you are OVERCHARGED). Digital gauges read stable and have better resolution than analogs. TIP: If you do not calculate superheat and subcooling from either a set of gauges like the Testos or from a refrigerant / pressure chart, YOU ARE GUESSING AND ARE CLUELESS. It is either that or weight in the specified charge with electronic weight scales from zero. If refrigerant leaks out again, I will have to leak search in the cabinet and at the water outlet for escaping R410A. You have to be careful not to suck up water in the sensor of the leak detector.