The moisture build-up will end up causing corrosion to your unit and blockages to your drainage system
An outdoor air conditioner is designed to be an all-weather device. Nothing should impede its airflow since heat transfer from the indoor unit to the outdoor HVAC equipment requires that this outdoor system radiates energy to the atmosphere. You could damage your HVAC system when you cover or block the outdoor unit. You may have thought of protecting your air conditioner during the off-season to prevent elements of weather from destroying your unit, but your outdoor unit is designed to withstand. Any dirt or dust that may gather on your air conditioner is washed away with rain and snow. While you may think that rain and water will destroy the unit, its internal unit is protected against water, and rainwater has a designated path to drain the water out to prevent your unit from accumulating moisture. However, you may need to cover your unit after summer to prepare for fall because your outdoor unit is not built to keep out debris, leaves, seeds, or nuts. During fall, leaves and seeds get into your outdoor AC unit, and this may cause moisture to build up to where seeds and debris have accumulated. The moisture build-up will end up causing corrosion to your unit and blockages to your drainage system. If you choose to make your cover, it is advisable only to cover the top of your outdoor AC unit. Covering the entire unit will lead to moisture getting trapped inside, which will cause your unit to rust and corrode. When you fully cover up your unit, you will have provided rodents a place to stay instead of repelling them away.