THIS PROCEDURE MUST BE PERFORMED BY A QUALIFIED TECHNICIAN.
THIS PROCEDURE MUST BE PERFORMED BY A QUALIFIED TECHNICIAN.
Er04 indicates the discharge air sensor temperature is out of normal operating range. The error generally indicates a dirty or defective sensor, a short or open in the wiring, or a circuit board which is out of calibration. Normal operating range is 25°F/-3°C to 175°F/79°C. Verify accuracy of the discharge air sensor by reading resistance across the sensor wires. Compare the resistance reading to the value in Location 112 (L112) and the Discharge Air/Water Temperature Sensor Resistance chart. Make sure the discharge air sensor wiring harness is connected properly. In 4100 Series the harness runs from the sensor on the supply air blower assembly to the brown wires on the 15-pin harness on the control board (PSC) or the "Air" terminals on the LV circuit board (ECM). The sensor is not polarity sensitive.
NOTE: The replacement discharge air sensor has a conformal coating to help eliminate cleaning of the sensor.