Why does the airflow become weak or stop during heating operation?

At the beginning of heating operation, the indoor unit operates at very low fan speed for about 3–5 minutes while it warms up internal parts. The indoor unit also temporarily stops for a maximum of 15 minutes to perform automatic defrosting operation, during which the OPERATION indicator flashes. Additionally, if the room temperature rises above the set temperature in HEAT mode, the outdoor unit stops and the indoor unit operates at very low fan speed. (Pages 4, 11)