I have a 20 yr old RUUD A/C system. The unit outside works fine. Inside the Blower works great when the temperature in the house is over 70 or so. But at night we turn it down a little to 68 and evenutally the blower's output decreases dramatically. Air still comes out of the vents but it is 75% less than it usually is. Also the line coming in from the house from the condenser gets iced up. Any help or ideas would be appreciated. I replaced the filter recently and that hasn't helped.