The power supply is suppose to suck air from inside of the case and blow it out the back of the PSU (i.e. the side where the AC outlet and main power switch is located) if it's a top mounted PSU.
If the computer case supports a bottom mounted PSU, and the case has vent holes on the bottom where the PSU is mounted, then the PSU is supposed to be installed with the PSU fan facing down against the vent holes so that it is able to pull cooler outside air through the PSU. Just make sure that the computer case is not sitting on a carpet or on a surface that will block the computer case's bottom vent holes.
The Corsair CX750's 120mm fan is an intake fan. If you place your hand near its fan you should feel air being sucked into the PSU. If you feel the fan blowing air out of the PSU then you should contact Corsair and have it exchanged for one that works properly.