There may be a variety of issues causing the warm air flow or there may be one main issue. The first thing to check is the freon level of your central AC unit.
Phone a certified HVAC professional in your area and schedule a service call to come out and check your freon levels. If your freon level is low, odds are you have a leak in the unit and it will need to be found and repaired. The performance of your unit will only get worse as more freon escapes.
Other issues that may be causing poor performance may be found in your ductwork, attic insulation levels, and attic ventilation.
- If your ductwork is leaking, cool air is escaping into your attic before it reaches your air vents.
- If your attic insulation level is low, cool air is escaping into your attic faster than than your unit can keep up with.
- If your attic is not sufficiently ventilated with enough attic and eave vents, the air in your ductwork is being overheated before it reaches your interior air vents.
If your AC's freon levels aren't the cause, you may consider having an energy auditor evaluate the performance of your ductwork, insulation and ventilation.
For more information:
Read Steve Saunders' Q&A "I keep hearing that I should get a home energy audit. What should I expect to pay and expect to get?"
Alsovisit the Department of Energy website.