Heating tune up performed today on a Carrier heat pump with air handler installed in 2020. All electrical connections are tight with no corrosion. Heat strips are pulling proper amperage. ECM blower motor is acceptable. Blower wheel and evaporator coil are clean. Biological growth is starting to form on the inside of the air handler. Highly suggest adding a germicidal light to kill existing bio growth and prevent it from coming back. Compressor and condenser fan motor are acceptable. Refrigerant levels are in range. Reversing valve and defrost control board are working appropriately. Outdoor unit was washed and waxed.