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 an open discharge air sensor, a short in the wiring, or a processor control 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 sensor reading to the value in L112 to verify proper calibration of the processor control board. Make sure the discharge air sensor wiring harness is connected properly. The harness runs from the sensor on the supply air blower assembly to the DS and SC terminals on the terminal block (PSC) or the "Air" terminals on the low voltage circuit board (ECM) in the furnace.