A lot of people, especially TB people refer to a crypt orchid as a 'ridgling' or a 'rig'.
You should first have a blood test run to see if he has high testosterone levels. If he does, he more than likely has a testicle (or two) that has not descended. Sometimes you can hold them off of feed for 24 hours to empty out the gut and a good Vet can do a rectal palpation and can find the testicle. If it is near the inguinal ring at the top of the scrotum, they can sometimes lay the horse down and pull it through where he can be castrated.
If it is up high or can't be found, they have to do abdominal surgery to find it and that can run $500.00 to $1000.00 or more.
Does he have a loose flap of skin high between his hind legs that would indicate he has at least had one removed? If both are still up, it can be even more expensive and complicated.