If your home's central air conditioner is blowing air but it is not cold, then your air conditioner is having a mechanical problem that you need to diagnose and fix. The good news is that there are only a few problems that can cause your air conditioner to blow warm air -- and many of them are simple for you to fix. To this end, here are some tips for diagnosing and fixing some of the most common central air conditioner problems:
Tip: Check the Outdoor Compressor for Blocked Vents or Obvious Damage
Since your air conditioner's cold air is cooled in the outdoor compressor unit, that should be the first thing you check when your system is blowing warm air. Make sure that the compressor is not blocked by any vegetation and that it has not suffered any damage. If you find the compressor's vents are clogged, then use your shop vacuum to clean them out before you proceed with troubleshooting.
Tip: Check to See if the Air Conditioner's Coils are Frozen
While you are at the air conditioner's compressor unit, look along the bottom of the unit to see if the metal coils are frozen or covered in ice. If the coils are frozen, then turn on your central air system on "fan" only and let the system run until the outdoor air temperature has melted away the ice. Once the ice has melted, then your air conditioner should blow cold air again.
Tip: Clean and Drain Out the Water Condensation Pan
Below the coils on your air conditioner's compressor is a flat metal pan. This pan collects the water condensate that runs off of the unit's coils. If the pan's drain becomes clogged, then the pan will grow mold and can cause problems with the system's function. Remove the pan and wash it out with a solution of household bleach and water. Use an old toothbrush to clean out the drain so that it will flow well again. Make sure you dry the drain pan well before you reinstall it.
Tip: Consult with a Professional HVAC Contractor if Necessary
Finally, if none of the solutions above have restored your air conditioner's cold air flow, then you need to have the system checked out by a professional HVAC contractor who offers air conditioning repair. Your air conditioning unit may have a bad internal fuse or coil problem where you cannot safely or easily repair it yourself.