if u have the settings at AUTO then yes it will only run untill the the temp is high enough to which u set the tempature at aka 80+. Use the setting manual if u want them to come out right away and blow out cold air untill the car warms up. Read your maunal for the AUTO temp control.
If u have the inside temp set at 80 or 78 then thats the temp will have inside it will not be 78 comming out of the vents.