Carlen coached the West Virginia Mountaineers from 1966 to 1969 with a record of 25–13–3 (.658). Then he coached the Texas Tech Red Raiders from 1970 to 1974, where he amassed a 37–20–2 record. From 1975 to 1981, he was the head football coach of the South Carolina Gamecocks where he coached Heisman Trophy running back George Rogers and compiled a 45–36–1 record. Carlen 45 wins are third most in the program's history after Rex Enright's 64 and Steve Spurrier's 55. In 1979 and 1980, Carlen led the Gamecocks to consecutive 8–4 campaigns with appearancess in the Hall of Fame Classic and Gator Bowl. His career bowl game record is 2–5–1.