A control system for mounting to a vertically-extending rail. The control system includes a plurality of bases, each having a channel formed therein that is adapted for mounting to the rail. A plurality of modules are provided for removable mounting to the bases, respectively. Each module has circuitry for processing control signals and a housing enclosing the circuitry. At least a bottom end of each housing has openings therein to permit air to flow into the housing and over the circuitry. A plurality of air flow deflectors are provided for mounting to the bases, respectively. When the modules and the air flow deflectors are mounted to the bases, the air flow deflectors form pockets with the bottom ends of the modules. The pockets have enlarged openings disposed parallel to sides of the modules.