I have noticed some time back that my A3 Formaldehyde sensor is always zero and checking behind i`ve noticed that it was always zero. I believe it is not normal as VOC, for example, it is always oscillating?
As electrochemical sensors have cross-sensitiviy to certain chemicals, you can trigger a false positive using some alcohol . Put a piece of textile soaked in alcohol close to the A3 inlet, and check the formaldehyde readings . They should begin to rise shortly, indicating the sensor is functioning.
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