Why is indoor humidity high while the AC runs? The symptom narrows the next observation but does not identify a failed part. For the heating and cooling system, first separate what the thermostat or normal controls request from what the indoor and outdoor equipment actually do. Note airflow, temperature change, timing, sound, odor, visible water or ice and whether the problem affects one room or the whole home, without opening a panel or reaching into equipment.
Evaluation can combine calibrated indoor moisture readings with runtime, airflow, coil condition, condensate removal, ventilation, duct, and envelope observations instead of treating the thermostat reading as a diagnosis. Ask for the moisture and operating measurements behind any recommendation and clarify whether drainage, controls, ventilation, duct work, or separate moisture-source repair is included. Seasonal humidity, groundwater, coastal exposure, ventilation codes, and building-envelope practices differ widely, so a national moisture target is not a property finding. Record when the home feels damp, whether cooling reaches the setpoint, any window or duct condensation, bathroom or kitchen exhaust use, water intrusion, and whether the change follows recent service or weather. Humidity that rises only during mild wet weather differs from persistent moisture with long cooling calls, rapid cycling, ventilation changes, or a building leak unrelated to the AC.