A giant ball of ICE hits a star

vorcil

What happens?

pallidin

Well, long before it would "hit" our sun, it would start to "boil-off"(think comet tail)
But if it were big and fast enough perhaps part of it could survive until outer impact. But I doubt there would be any net effect on the sun.
The processes our sun goes through are much more violent than it's reaction to a moon-sized ice ball hitting it.