I've got a 3 ton Trane a/c unit that produces about 20 degrees difference from return to supply. I measured this by inserting a thermometer at the return and then setting same thermometer into the various supplies throughout the house. Once my A/C system comes on it basically stays on till evenings when everything cools down. I have a 1/3 HP blower motor set up to use the highest speed possible for cooling. For heating system works fine. Contractors just want to replace the HVAC system with a new one. My a/c system is working just not putting out the cold air that it has inside. My system's return is 128 sq inches - while the supply is 364 sq inches - Is this imbalance my problem? Can I use a faster blower fan to overcome this problem? What to do?