Performed preventative maintenance for 6 year old air conditioning and heater system. Inspected all the electrical components. Confirmed proper high and low voltages. Customer replaced the air filter recently (16x25x1). Tested the temperature split between the supply and return. System is operating at a 20° differential on a 68° day. Tested the amp draw for the blower, compressor, inducer and fan motor. All were operating within the manufacturer specs. Inspected the drain piping for clogs and pump operation. Short Drain pipe is clear and pump works as it should. Inspected both the evap and condenser coils. Both are fairly clear at this time. Tested the temperature rise for the heater. System has a rise of 68°. Made sure all tubing to the collector box was clear of debris. Performed a combustion analysis on the furnace. System had a CO level of 17ppm. System is operating properly at this time.