The answer to 'tune-up blowing cold air' is that this issue is often caused by a problem with the HVAC system's refrigerant charge. If the system is low on refrigerant, it can cause the airflow to be cold instead of the desired warm air. This could be due to a refrigerant leak or an improper initial charge during installation.
Other common causes include a malfunctioning thermostat, clogged air filters, or issues with the blower fan. Troubleshooting these problems may require the expertise of a professional HVAC technician, especially if the issue is related to the refrigerant system.