[xTool AP2] Improve airflow monitoring and error handling

Hey, just wanted to share something weird I’ve been dealing with and see if anyone else has had the same thing happen. My AP2 started giving me the error **M9039 S4** whenever I switched the fan to level 4. Level 3 was totally fine. I went through all the usual troubleshooting with support, cleaning the cyclone, checking all the filters, removing them one at a time, the whole routine. Out of curiosity I removed the **first pre-filter** completely and tried again. And suddenly the AP2 works perfectly, even on level 4. No error at all. The moment I put that pre-filter back in, the error comes back immediately. So it’s pretty clear that the AP2 itself is fine and the issue is just that one filter restricting airflow too much. I explained all of this to xTool support, thinking they would just send me a replacement pre-filter. But their technical team says the entire AP2 needs to be replaced and they want me to return the whole unit. Even though the machine works perfectly without that filter. So now I’m wondering if anyone else has dealt with something like this. Did they really swap the whole AP2 for you even if the problem was just a bad filter? Or has anyone actually gotten them to replace only the filter? Curious to hear how others handled it. I’d like to avoid being without the AP2 for weeks if it’s something this small. **Update:** A little follow-up because things turned out way stranger than I expected. xTool actually sent me a full replacement AP2 in the meantime. The new one arrived yesterday, so I plugged it in right away. And… the exact same error showed up again within a few seconds on fan level 4. So at that point it was pretty obvious the original AP2 wasn’t the actual problem. That’s when I started testing everything piece by piece. First I disconnected the AP2 from the M1 Ultra completely. It ran perfectly. Then I tried it with and without its own pre-filters. Also fine. Then I attached the hose to the M1 Ultra very loosely. Still fine. Fully locked in? The error came back. The weird part: all of this kept pointing to some kind of airflow restriction, but not inside the AP2 itself. So I checked the round fabric filter inside the M1 Ultra (the little white disc above the exhaust port). If that thing is installed, the AP2 eventually throws the error. If I remove it, everything works. To make sure the filter wasn’t just old or dirty, I used a brand-new one. At first it worked, but after about 30 minutes of engraving/cutting wood, the new filter became clogged enough to trigger the same error again. So basically the AP2 is fine, both units behave the same, but the M1’s fabric filter gets restrictive incredibly fast and causes the AP2 to freak out on level 4. Replacing that filter every half hour obviously makes zero sense.