Why does both the indoor and outdoor units of my Heinner HAC-12OWF-BK Air Conditioner make noises?
- RRobert FieldsSep 12, 2025
A low hissing sound during operation is normal and is caused by refrigerant gas flowing through both indoor and outdoor units. A low hissing sound when the system starts, has just stopped running, or is defrosting is also normal and is caused by the refrigerant gas stopping or changing direction. Squeaking sounds can be due to normal expansion and contraction of plastic and metal parts caused by temperature changes during operation.