Refrigerant is the fluid inside your AC condenser that cools air passing through the system. When this fluid is too low, it can lead to an air conditioner that isn’t cooling! Look for these signs to spot low refrigerant: Hissing or bubbling sounds from your AC unit. Ice is forming on refrigerant lines. Air is blowing, but it’s not cold. Air conditioner tune-ups give our HVAC techs a chance to check refrigerant levels. You don’t want to be caught without working AC on the hottest days! So help your cooling system with an annual tune-up.