When AD < AS, it means planned demand is less than planned supply. So there will be unintended accumulation of inventories. This will result in fall in supply. These changes continue till AD and AS are equal.
Detailed Answer:
When Aggregate Demand is less than Aggregate Supply at full level of employment, there is deficient demand in an economy which leads to deflation. The price level will come down which in turn reduces the AS and ultimately AS will be equal to AD.
