Partially Open Sensor

System will operate in heat mode most of the time or all the time. A new sensor may be substituted for a doubtful ambient sensor. To check for a partially open ambient sensor, disconnect service connector and check resistance across the two dark blue wire terminals (female insulator). Maximum resistance should be approximately 650 ohms at 65°F, 550 ohms at 75°F, and 450 ohms at 85°F. If resistance is constantly 1500 ohms at the various temperatures, sensor is open. If resistance values are consistently higher than those above, shunt resistor is open. In either case, replace sensor.