What happens
Duct restrictions or leakage prevent the useful air delivery needed for comfort and coil loading.
Typical symptoms
Some rooms remain warm, unusual return noise or measured airflow outside the system requirement.
Checks that distinguish this cause
Check accessible return and supply paths, dampers and leakage; compare static pressure and measured flow with the unit's airflow tables.
What can look similar
An oversized system can also make uneven comfort and short cycles; diagnose delivery before resizing equipment.
Repair direction
Correct the verified duct or distribution defect with an appropriate design.
Verify the repair
Verify delivered airflow and room performance under representative conditions.
Equipment-specific limits
Thaw ice safely and establish airflow before charge diagnosis. Never chip ice or operate cooling indefinitely without the blower.
Practice this diagnosis
This cause is a reference topic; it does not yet have a dedicated simulated call. Browse the practice board.
References and applicability
Original HVACSim explanations with manufacturer and instrument-maker references for further reading. These resources support the subject; their model-specific examples are not specifications for every system.
- Copeland: Refrigeration basics: troubleshooting fundamentalsCompressor and refrigerant troubleshooting concepts, not a charging specification.
- Carrier: HVAC installation and commissioning overviewSizing, airflow, charge and A2L installation considerations; obtain the exact unit manual.
Editorial review: 2026-09-29. Verify the current manual for the installed model.