In very dirty environments, it can be advantageous to have a small amount of compressed air entering the control panel when the panel cooler is not operating (turned off utilizing a solenoid and thermostat package to conserve energy). This is a "constant purge" system that will keep the control panel at a slightly positive pressure continually to prevent dirty environmental air from entering, thereby keeping the control panel clean. This reduces cleaning maintenance and can extend the life of the controls.
One way to do this is to drill a small hole in the solenoid valve but that would be illegal in many jurisdictions or at least against many corporate policies since that would compromise the tested electrical approval integrity of the solenoid. In addition, larger control panels many need to be "purged" with more air flow while small panels only require a negligible amount.