Is this Fafco valve actuator actually a Jandy?
If you can't manually operate the handle, the actuator might not be at fault - the actual valve might be jammed (or the actuator might be jammed, keeping you from operating the valve by hand, I guess.)

In any case, you should probably take the actuator off and verify if the valve can be operated by hand without it in place - if not, the new one won't have much joy either.