An air source heat pump has two main parts - the condensing unit installed outside of the house and the evaporator installed inside the ductwork. For a heat pump to work up to specs, or sometimes to work at all, these two components must be properly matched. Each condenser works properly with only a limited number of evaporator models. Each of the matches has a unique identifier -- the ARI reference number. Think of the ARI reference number as the marriage certificate for the components of your heat pump. It's that simple.
On the invoice, among other information, you contractor must show three crucial pieces of data – the model number for the condenser, the model number for the evaporator, and the ARI reference number. Before the evaporator gets concealed inside the ductwork for good, check that the model number on the evaporator matches the number on the invoice. Do the same for the condenser.
Now, go to http://www.ceehvacdirectory.org/hp.php?reset=true At the very top of the page, type into the window the ARI reference number from the invoice. Click “Search The Database”. This is the moment of truth. The site will give you the model numbers for the condenser and for the evaporator, as well as the SEER rating for the heat pump and its cooling capacity. Do they match the numbers on the invoice? They'd better to. If they don't, do not allow the contractor to proceed with the installation. Do not accept ANY excuses. That would be my best advice to you.
About ARI. It stands for Air-Conditioning and Refrigeration Institute. ARI is a trade association that represents the manufacturers of more than 90 percent of the air conditioning and commercial refrigeration equipment installed in North America. An internationally recognized leader in developing standards for these products, as well as certifying their performance, ARI is also a major advocate for the heating, ventilation, air conditioning, and refrigeration (HVACR) industry both domestically and abroad.