Performed preventative maintenance for a carrier furnace. I observed the system starting normally. The supply temp is at 128°F. The blower motor amp draw is within normal range. I observed the system shut down normally. Checked all electrical components needed for heating. Evaporator coil is clean. Drain line is clear of clogs. Replaced the air filter size 14x20x1. Condenser coil's are clean. Amp draws are 5.6 for the compressor and .3 for the fan. Refrigerant pressures are within normal range for the outdoor temperature. The system is operating properly at this time.