There are few applications requiring more accurate and stable temperature, humidity, and pressure control than that of clean rooms for manufacturing integrated circults. Maintaining the temperature and humidity at the same levels during all steps of the manufacturing process considerably improves "good chip" yield percentage. Electronic analog controllers, sensors, and actuators have been successfully applied to these critical control requirements in both new installations and the retrofit of existing pneumatic controls. This paper discusses the successful application of these control systems at several semiconductor plant installations. Areas of caution are addressed and installation experiences reported. The paper includes some observations and recommendations that were found by the authors to be relevant in the design and installation of these specialized HVAC control systems.