How do you keep your basement and main level a more even temperature. Our furnace guy was here yesterday and he said to leave the fan running all the time. I think that would drive me crazy but he claims it is the only way to have a more even temp between the 2 floors.
If you have some time to spare, try adjusting your dampers or diffusers. If some areas seem to have a lot of airflow, adjust the dampers or diffusers closed a little. This will force more air somewhere else...hopefully where its needed. You really shouldnt need A.C. in the basement, so close them first, then move up to the main floor...etc. Make sure your blower is running at high speed.
Its called balancing your system. Check the filter. If the system WAS cooling the upstairs, and now it doesnt, you may need the evaporator cleaned, pet hair, dust and debris may restrict air flow over time.