HVAC pros

We just installed a Carrier dual Stage Heat Pump/AC System . Our 12 year old American Standard would run 24/7 to keep the house at 80 when it got above 100 .The Carrier keeps it at 78 and runs less than 3/4 of the time . The old one was undersized at 2 /1/2 Ton 8 Seer where the new one is 3 ton 18 Seer.