We have a 3 year old unit that is not blowing cold air when we switch to cool. The unit outside starts up and everything seems fine. But it does not blow cold air. The second identical unit we have blows very cold air. Please help.;)

Could have developed a leak. Could also be dirty coils.

Have you had the freon checked. Are you sure that the compressor is running or do you just hear the fan motor outside running.

If it's not cooling and the compressor is running, call your service company, don't run the unit anymore. You are probably low on refrigerant and you can damage your compressor if you run it with a low charge.