If your AC isn't turning on, that's a sure-fire indication that something is wrong and it's time to contact a professional. However, like cars, air conditioning systems often give warning signs before a full breakdown occurs. Knowing how to spot these red flags can save you a whole lot of discomfort, stress, and money in the long run. Call your local HVAC company when you spot these signs: AC not blowing cold air Weak airflow Malfunctioning thermostat Excessive moisture or leakage Unusual sounds Foul odors Low refrigerant levels Unexplainable utility bill increase Read more on how to troubleshoot common A/C issues that plague homeowners.