In the heating process, why does the indoor unit stop air supply for a period of time and then turn on automatically after a few minutes?

The air conditioner is defrosting. 

When the air conditioner has been running for a period of time, the outdoor condenser will have a very thick frost and snow. It would directly affect the heating performance. Therefore, when the air conditioning operation meets the defrosting conditions, the air conditioner will start to defrost. During the defrosting period, the indoor unit will stop blowing.