How many people have had their heat pump’s compressor fail? How many live at the beach where the corrosive winds destroy the exterior of your outdoor unit? The solution seems natural. Buy a new outdoor unit and reuse the indoor unit. The blower section works so why would you want to pay to replace it? The reason is that the new, more efficient outdoor unit will not work with the old blower section. The issue that arises is the pressure problems in heating mode. In heating mode the compressor sends hot gas to the blower section to be condensed. The heat given off by the condensing gas is then taken by the blower and dispersed, thus heating the structure. Old blower sections in air handlers are paired with smaller, less efficient coils. These coils are not rated to handle the hot gas being given off by the new, efficient outdoor unit. Because of this fact the pressure can reach dangerous levels. I have repaired two heat pumps this winter that had to have some refrigerant removed because the pieces of equipment were mismatched. It can destroy the compressor, cause refrigerant leaks and void your new outdoor unit warranty. Always replace your indoor unit when possible so you can get the most from your HVAC heat pump system.