The answer to 'tune-up blowing cold air' is that there are several common causes, including a refrigerant leak, a problem with the thermostat, or an issue with the compressor or other HVAC components. Symptoms may include the system blowing cold air at first but then switching to warm or hot air, or the system running constantly without cooling the home effectively.
In many cases, the solution may involve a professional HVAC technician diagnosing and repairing the issue. Attempting DIY repairs on an HVAC system can be risky and may even void the warranty, so it's generally best to call in a qualified professional unless the problem is something simple like a dirty air filter that you can replace yourself.