Insufficient defrost cycles can be caused by faulty defrost control components, such as sensors or relays, or incorrect system settings. Verify that the defrost timer is set correctly and that the outdoor coil temperature sensor is functioning accurately. Check for refrigerant leaks or undercharge, which can reduce system capacity and lead to insufficient defrost cycles. Additionally, ensure that the system’s air filters are clean, as dirty filters can reduce airflow and prevent proper defrosting.