Don't stand right next to the object you want him to repair. He will think you want to do it yourself (and mostly say "Go ahead and try it").
Stand a few hex'es away from the object, click in your skilldex (button right bottom side of screem), click repair, click on the object.
Vic will walk towards it and (try to) repair it.
If this doesn't work, please post more info: Where are you (redding, den, vault city, ...) and what are you trying to repair?