Carrier heat pump with air handler installed stalled in 2017. All electrical connections are tight with no corrosion. Heat strips are pulling proper amperage. X13 blower motor is acceptable. Biological growth is present in the air handler installed stalled highly suggest adding a germicidal UV light to kill the biological growth and help sterilize the air. Compressor and condenser fan motor are acceptable. Refrigerant levels are in range. Reversing valve and defrost control board are working properly. A compressor saver has been installed. Attic insulation is adequate.