Would any missing parts cause the fans to run at full speed?

Hallo, I'm attempting to revive a 2011 13" Unibody (A1278) that's missing pretty much all its internal parts. Right now it only has a logic board, fan+ heatsink, battery and the antennas hooked up, in a shell with a broken screen attached. Other than a new cable for a drive it doesn't need any more parts because I intend to use it as a headless server, and I have managed to get it to boot and display to an external screen, but the fans run at full speed the moment I switch it on. Does anyone know if any of the components I'm missing have a temperature sensor that the board is upset it doesn't have? Or would this be a fault with the board itself? The CPU has been repasted so I doubt it's overheating.