Why is the heat pump not cooling? The symptom narrows the next observation but does not identify a failed part. For the heat-pump 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.
Note thermostat mode, vent airflow, outdoor operation, ice or water, and whether the same system heated normally before the cooling problem appeared. Failure to change modes differs from weak airflow, an outdoor section that does not start, or a system that runs steadily without removing enough heat. Technical diagnosis can evaluate thermostat signals, reversing controls, blower and duct airflow, coils and drainage, outdoor equipment, electrical operation, and the sealed refrigerant circuit. Ask the company to test both the mode-change and cooling-performance branches and to separate controls, airflow, electrical, and refrigerant work in any authorization. Cooling load, humidity, outdoor coil exposure, utility interruptions, refrigerant regulation, and permitting differ by climate and jurisdiction.