Abstract: Modulating system for electrically or pneumatically controlled chillers in which a sensor senses the space condition, in a controlled environment or space. Output signals from an enthalpy sensor or other sensor representing the space condition are fed to chiller modulator electronic controls and thence to the chiller modulator interface controls, be they electric or pneumatic. The sensor monitors the conditions in or returning from the controlled space or environment. By measuring both humidity and temperature, the enthalpy sensor generates an effective temperature or comfort level. The input signal from the sensor is compared to an operator adjustable set-point. If the measured condition is less than the set-point, an error signal is generated which is proportional to the difference multiplied by an operator-set sensitivity control.