For what controller? Trane, York, McQuay? It depends on the range of the sensor. Look in the IOM of the product you are looking at. They typically have a temperature/resistance chart to help. If you know the range of the sensor(10,000 ohms for example) and the coefficient(NTC or PTC) you can figure out the dc voltage for a given temperature. Plot it on a chart in Microsoft Excel if you know to use charts. Say the operating range of the sensor is -40 to 120 degrees F. The span is 120- -40 or 120+40 = 160.Now if the coefficient is positive than at -40 the dc voltage would be 2 volts. At 120 degrees the dc voltage would be 10vdc. At 40 degrees the dc voltage would be 6vdc. Smell what I'm steppin' in? If the resistance of the sensor goes above or below the range then the sensor will appear as failed to the controller. This would be a linear type sensor.