Performed AC maintenance on a carrier system. Units cooling temperature split is 22 degrees. Indoor amps are ok. Blower motor and housing are very dirty. Filter is dirty. Condensate lines are clear. Outdoor unit was deep cleaned. Starting components are in range. Compressor and fan amp draws are ok. Refrigerant levels are low. Customer said he wants to do research on adding refrigerant and doing maintenances himself. I advised him of the dangers. System was running st end of appointment.