I was out of town last week. We are in our 2nd summer in this house and I never thought the AC worked well last summer so I called a service company. I was out of town last week when they arrived. (We have two systems. The one for the upstairs cools well with 56 degree air coming out at outside temps of 80 degrees. Ot main floor unit barely keeps up if it is over 90 degrees outside and falls behind if a lot of traffic goes in and out of the house. I also note at any given time the air coming out of the vents on the main floor is 4-5 degrees warmer than the upstairs unit.) I also notice at any given time when both units are running the suction side of the upstairs system is much colder that the main floor unit. My wife had the guy talk to me when he was ready to leave and he said this. He suspected the fan speed was too high to properly exchange the heat from the house to the evaporator so he lowered the fan speed to the 2nd of 4 speed settings. (It was on high or 4) I will agree the air at the vents are cooler now, just wanting to know if this is a productive action to take? I have always noted a system fan runs much faster when cooling in the summer than heating in the winter and assume there is a reason for this.