How to Set up AirPods Pro 3 as Hearing aids

Your issue is extremely common — and happens because AirPods are not “always-on hearing aids.” Instead, they use Adaptive Transparency + Conversation Boost, which AUTO-detects voices and suppresses background noise (like your fan).

That is why the fan sound keeps disappearing.TURN OFF Adaptive Transparency

This alone will stop the “fan disappears” problem.

How to Set up AirPods Pro 3 as Hearing aids

Sorry I'm no expert in this area, yet your post to the community certainly deserves some response. At least we get your discussion thread under way, and provide opportunities for others to join in and share their expertise.

Fortunately Apple Support provides articles and other documentation to help us understand the features, and options, and to take control. You can dodge anything you are already familiar with, and choose what else you wish.

Customising the AirPods 3 to suit your own needs is important, and not everyone wants to use the same features,

Eg: If you haven't seen it already:

You may want to browse: : Use the Hearing Aid feature on your AirPods Pro 2 or AirPods Pro 3 - Apple Support

You may also want to experiment with switching modes, or turning them on or off, as you wish... "depending on how much of your surroundings you want to hear". See: Active Noise Cancellation and Transparency modes for AirPods - Apple Support

and

How to: Use Adaptive Audio with your AirPods - Apple Support

Eg: says:

"About Adaptive mode

Adaptive mode blends Active Noise Cancellation and Transparency mode together to control the level of noise you hear in your headphones based on the changing noise conditions in your environment. You can customise Adaptive Audio to allow more or less noise."

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Trouble-shooting, if needed:

What to do: If Active Noise Cancellation isn't working as expected on your AirPods - Apple Support

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You can "change what happens when you double-tap your AirPods or press-and-hold AirPods Pro and more."

See how to: Change the settings of your AirPods and AirPods Pro - Apple Support

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You can also: "Use Live Listen with AirPods

You can amplify sound with Live Listen. Place your iPhone or iPad near what you want to hear, then listen through your AirPods. This can help you hear better in some situations—for example, when having a conversation in a noisy environment." See how to: Use Live Listen with AirPods - Apple Support

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Resource: AirPods User Guide - Apple Support has all the info., on what else you can do.

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AirPods Support Website: (info. topics, resources, support, and contact options for your AirPods....)

AirPods Support - Official Apple Support

1. Turn OFF Adaptive Transparency
2. Turn OFF Conversation Awareness
3. Use Transparency Mode permanently
4. Increase Transparency Amplification in Accessibility settings

Thank you kindly for taking the time to reply, and to let us know. All the best!