Performed heater tune-ups on two Carrier two stage gas furnace systems. Checked the electrical, mechanical and performance systems of the units. Replaced all return air filters with client supplied filters. Cleared, cleaned, flushed and treated the drain lines and cleaned the exterior of both furnace systems. Homeowner mentioned she felt like the upstairs system did not cool properly during the summer. I changed a few settings on the upstairs thermostat and also adjusted the airflow setting on the furnace.