Heat performance tuneup times two systems. Upstairs system is brand new. Found no issues with it at this time. downstairs system is 20 years old. The condenser is a 2012 model. I was recording 10 to 11 ppm CARBON MONOXIDE after the heater had ran for about five minutes. This exposure is dangerous to small children. I advised Lindsay that it would be best to replace now. She stated they are still paying for the upstairs unit. Downstairs heat exchangers have small cracks allowing CO into the airstream. Inspect blowers, evaporators and ductwork. Another recommendation today is to have the ducks cleaned. This will ensure the cleanest air is available for the home. Also checked the outdoor units to see if there were any issues when clients turn on the air conditioners. Run capacitor was 45+5 µF.