Performed preventative maintenance for air conditioning and furnace. Replaced the customer supplied air filter (14x30x1). Inspected all the electrical components. Cleaned the flame sensor, burners burner compartment and inducer port. Tested the amp draw for the blower, inducer, fan motor and compressor. All were above average but within the rated load. System is fairly old. Tested the temperature split between the supply and return. System is operating at a 17° differential. Performed a combustion analysis on the furnace. System is operating at 78.8% efficiency with a CO level of 54ppm. No CO present within the air stream. Systems is pretty old (25 years) and air conditioning doesn’t look to be in the best shape. Temperature split is not bad but not where it should be. Would recommend a system upgrade in the near future to prevent any major failure during extreme temperatures. System is operating properly at this time.