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Error code reference
Aprilaire HVAC Error Codes
9 error codes documented with diagnostic procedures.
Have your model number? Get codes specific to your unit.
E1Internal RH/Temperature Sensor open or shortedE2High Refrigeration PressureE3Model 76 Remote Control Communication LossE4Insufficient CapacityE5High Temperature Sensor Thermistor FailureE6Low Temperature Sensor (Frost Sensor) Thermistor FailureE7Float Switch OpenE8Inlet Air Temperature Out of RangeE9Outdoor Temperature Sensor Failure
Get the full diagnostic procedure for any code
Step-by-step tests, expected values, wiring diagram references, and verified part numbers.
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Common questions
How do I find the error code on my Aprilaire HVAC?
Most Aprilaire hvacs show the code directly on the control panel display. If your model has no display, it can be read by entering diagnostic mode with the key sequence for your model. The full procedures include model-specific instructions for reading codes.
Are these codes specific to my model?
The codes here apply broadly to Aprilaire hvacs. Meanings and diagnostic steps can vary by model and production year, so enter your model number for model-specific information and procedures.
What do I do if my code is not listed?
Some codes are model-specific or only appear in diagnostic mode. Enter your model number to get codes specific to your unit, or contact us. We update the database continuously from manufacturer service documentation.
How much does it cost to access the full diagnostic procedures?
A 3-day pass is $9.95 one-time and gives full access to all brands, codes, and procedures. Monthly access is $29/month with unlimited access to everything including Max AI diagnostics.