AC performance tuneup times five systems that started in May. I was delayed due to the weather. All of inside was completed on previous visit filters change, drains cleared inspections. Check charge on units. I added 3 lbs R 410 A to the older units that is in the basement. Upon arrival I did a carbon monoxide test on The basement unit. Found for parts per million when heater is running and second stage. Not an emergency but advise Jeannie that System will more than likely need to be changed next year.I also used wood from the basement to level out all four condensing units.