Typical signs
- Weak registers, whistling, very short cycles, icing or uneven temperature.
Where it is often found
- Furnaces, heat pumps, air conditioners, HRV/ERV units and duct systems.
What it can mean
- Loaded filter, closed register, crushed duct, dirty coil, refrigerant charge or sizing.
What to check next
- Check accessible filter, grilles and settings.
- Record cycle duration, temperature and outdoor conditions.
Reasonable immediate actions
- Clear filters/grilles and stop use if there is noise, burning or heavy icing.
When to stop and call a professional
- Refrigerant, combustion, motor, wiring, persistent icing or unresolved comfort.
Prevention
- Suitable filters, maintenance, balancing and verified sizing.