At the crest of the hill, the sled is at the highest point of its motion. The direction of the sled's acceleration at this point will depend on whether it is moving up the hill or moving down the hill.
If the sled is moving up the hill, the direction of its acceleration at the crest will be downwards, opposite to the direction of its velocity. This is because the sled is decelerating as it climbs up against the gravitational force pulling it downward.
If the sled is moving down the hill, the direction of its acceleration at the crest will be downwards as well. However, in this case, the sled's velocity and acceleration will be in the same direction. The sled is accelerating due to the gravitational force, which is pulling it downward and causing it to gain speed.
In summary, at the crest of the hill, the sled's acceleration will be downward, regardless of whether it is moving up or down the hill.