Administrative Processing for Unmarried Son/daughter of Permanent Resident

[falamtauko]

I have been helping my friend, who has a son in Kathmandu,Nepal. They have gone through all the processing and filing of immigrant visa for their son who is over the age of 21. Son has gone through visa interview and US embassy has been holding his passport. The case is under administrative processing. It has been 4 months now, if we try to get in touch with embassy they say we will call/inform the son about what has happened about immigrant visa. Does any one have idea how long it might be of this administrative processing?

What can we do? can we get in touch with our local congressional representative/Senator? Any information on this will be very welcomed.