Performed A/C maintenance on a carrier heat pump. Cooling split is only 15 degrees. Outdoor unit was cleaned. Indoor coils are clean. Condensate lines are clear. Indoor blower is clean and amping in range. Refrigerant is low. Customer wanted to proceed adding refrigerant rather then dealing with the builders. I charged system to find spiking subcool and pressures indicating air in the system and a bad TXV. Customer is contacting the builders to move forward with the repairs. Home is less than a year old. System was cycled before departure.