Aprilaire HVAC Error Codes

9 error codes for Aprilaire hvac models. Each links to the full diagnostic procedure from the service manual.

CodeDescription

E1Internal RH/Temperature Sensor open or shorted E2High Refrigeration Pressure E3Model 76 Remote Control Communication Loss E4Insufficient Capacity E5High Temperature Sensor Thermistor Failure E6Low Temperature Sensor (Frost Sensor) Thermistor Failure E7Float Switch Open E8Inlet Air Temperature Out of Range E9Outdoor Temperature Sensor Failure

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M+

M+ Max·Aprilaire HVAC

E1 on my Aprilaire HVAC

M+

Internal RH/Temperature Sensor open or shorted

From Service Manual 935165, p.17:

1.Turn off power, remove User Interface Assembly, check connection between sensor board and control board; if connection is okay, replace the RH Sensor board (5460).

2.Disconnect the sensor and measure resistance at the sensor body. Expected: 10 kΩ to 12 kΩ at 77°F (25°C).

3.Check the sensor harness for opens and shorts. Back-probe the sensor pins at the control board connector; a reading outside 5 kΩ to 50 kΩ indicates a failed sensor.

Part WP8577274

Temperature thermistor

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