I have a bunch of AMS 2 Pro units, and a bunch of AMS HT units. The AMS 2 units stay dry like the Sahara. The AMS HT units never get under 10%, and pop right back up to about 20% / 25% after a day or so.
Everything is dried, some filaments for several cycles
The room has a large dehumidifier, and is kept at a constant 30% RH
I was hoping to keep my engineering filaments in the HTs and not have to worry, but it looks like I am going to have to do some kind of constant musical chairs with my spools, which would be a pity and also a waste of money - I bought these things to not have to worry about that kind of stuff.
Anyone have similar experiences, or suggestions on how to improve the situation?
I have never gotten mine to stay dry either. My guess is due to the lack of desiccant storage space (can only fit 1–2 packs) and the airtightness (or lack thereof). For most engineering materials, though, I always dry right before printing to ensure good results, which also dries the AMS HT in the process, so it hasn’t been a major issue for me.
I am having a similar issue (same setup with dessicant holders) which I have explored with some tests and some customer service, not fixed yet but might be able to help diagnose or at least acknowledge the issue.
I own 2x AMS 2 Pro which both show <5% humidity. While I’ve read that most sensors cannot accurately report <10%, I have filled them to the max with dessicant and never open them, so I think it is a correct value.
However, my AMS HT (on the same shelf) constantly reported 15-20%, even when I emptied the AMS HT and filled it to the max with about almost 1 Kg of new dessicant bags.
To test:
I placed 3 different humidity meters in the AMS HT, they all showed 10% (which is the lowest they will go).
I filled them with 1 kg of dessicant
I checked the seal (the rubber edge which seals the lid should be straight and not curved/bumpy
I ran a 12 hour 85 degrees drying run, humidity dropped almost nothing, maybe 2-3% and went right up afterwards.
After these tests, I contacted Bambu, shared the log file of the drying and they sent over a new heating element which included a new humidity sensor.
The installation took about an hour (very simple but annoyingly small wires and plugs take up the most time). Now I’m doing the same tests and it does not seem to drop below 12-13% for 2 days now. Due to the large amount of dessicant, it can also not really go up if it’s leaking.
Conclusion: My guess is that the sensor the AMS HT is either really bad (15% too high) twice in a row, or that there is somehow a sort of leakage which is not present in the AMS 2 Pro.
I would try to first confirm the value reported by the AMS HT to see if your unit’s humidity sensor is correct. I used both the Bambu humidity meters (the 3-4 euro things) and a room sensor by ThermPro (Amazon). This way you can see if it’s a sensor error.
If the value is correct, I would check (or maybe improve, if possible) the seal on the device.
I would also definitely contact Bambu. Based on our experiences and also that of others on the forums, I think something is wrong with (some?) AMS HTs.
Please let us know if you (or anyone else) has more information or suggestions! Good luck.
I’m posting in this topic as I don’t currently have permission to create a new topic. I’ll let an admin more or delete this as they see fit.
I have a new AMS HT with a humidity sensor that was not reading correctly. After disassemble, I discovered the temporary tape cover, used to protect the sensor during assemble, was never removed. After removal, the unit worked as expected. It’s possible they made a parts substitution and only a few units have the temporary cover versus a permanent membrane. Or, maybe someone assembling the unit made a mistake. it’s worth a look to verify.
I was just going to post this - I got 3 HTs and 2 of them had tape in the same place, it is clearly a sealing problem because if you get a basic plastic sealed box and remove the humidity it’ll stay dry for a while
I would also check the rubber seal - The HT is great but QA seems to be lacking, I had similar problems with one of my AMS, the rubber seal was not seated properly so it wasn’t sealing
This picture is from the Wiki; section 6 – “Install the AMS HT Heating Unit”. I placed a white circle around the humidity sensor PCB. The PCB is removable.
That’s a strange place for “packing” tape on that sensor… Thanks for bringing that up, I would have had no idea.
I have to open mine up anyway because a couple weeks ago the unit reported an “abnormal exhaust valve” error. I’ve had it since early Dec. '25, dried maybe a dozen rolls in it, mostly high temp and some lower. When I went to file a support ticket, I found it especially interesting that there’s a whole support contact category named “AMS Drying Air Vent Malfunction.” They sent a new valve out right away, but I haven’t replaced it yet (I knew I was waiting for something!). But seems like perhaps a common issue. Note that I could not tell any difference in the operation from before and after the error… all the clicks at the start of drying are the same. I’ll see if it acts any differently with the replacement. Point being that maybe it was bad to begin with… I wonder how sensitive the error detection mechanism is. The error started in the middle of a low-temp PETG drying session, after having just dried a roll of PC at high temps.
And BTW mine also never shows < 10% humidity, even in a room that is already 15%, while the AMS 2 Pro next to it is constantly < 10% (sometimes 0%). Extra activated alumina desiccant inside both units, besides the BL packets which are still orange. I chalked it up to sensor variation (and no published specs on the sensors in the first place), but I now I wonder.
sometimes it would chatter at startup and I think it would sometimes get stuck slightly open as I have two AMS HT and one would often be higher in humidity than the othe
eventually I got a vent error message it was stuck open and I managed to get it closed and a closed vent during heating will lead to condensation inside the AMS HT for drying something with a lot of moisture
in my case it was a bunch of wet dissecant
bambulab replaced the vent and things are back and running and I have a better understanding of the vent function
I think some of the difference between the AMS 2 pro and AMS HT in regards to reading humidity comes down to where the humidity sensor is located
I’m also having the same issues with the AMS-HT not being a sealed unit.
Firstly, the RH reading on the display never seems to get below 25% RH. I have confirmed it with another Hygrometer I placed inside the AMS-HT and it sits at 10%, so I’ve confirmed the drying cycle is functioning correctly.
Second, the RH just steadily rises after the drying cycle completes. I contacted support and they sent out a plastic base. I was expecting the base was to arrive with a new seal but no such luck. I replaced the base but have the same issue.
I have just today placed 3x layers of tape over the electric vents as from assembly I thought this could have been the issue but it appears to still be rising.
I think I’m just going to keep taping things up until I get the RH to level off to try and pin point the location of the leak ……. very frustrating !!
I think there are two factors with the Ams ht and getting low humidity.
one is that there is very little dessicant inside it
And the other is the humidity sensor location
I’ve been able to get below 10 on the sensor but only when putting in a lot of dessicant. I basically added in a containers on either side of the spool.
you can see when you start heating and circulating air with a lot of dessicant that the humidity will drop by 3 percent on the Ams ht.
do the same on the Ams 2 pro and the humidity goes up.
so if you dry something like pla which doesn’t absorb any water, when it is done the humidity will stay high as that little packet in the rear is totally inadequate to remove the moisture
I have the same issue. Got independent humidity monitors that can go below 10%. Put 1 in my ams 2 pro and 1 in my ams ht. The readings on these sensors matched the self reported values on the AMS units.
After weeks of back and forth with a support ticket and following all of their advice, they finally shipped out a replace case. It’s just the plastic bottom bracket without any new seals so I don’t see how this is supposed to fix the issue.
The problem seems to me an issue with seals and vents.
I haven’t disassembled the ams ht yet so I can’t confirm whether this replacement part will solve the issue.
Glad this is not just me - have the same issue with my AMS-HT.
I use my AMS-HT on my left nozzle (with 3x AMS 2 Pro on the right) on my H2C.
I’m actually considering selling my AMS-HT and replacing it with another AMS 2 Pro instead - use my external dryer to dry any filament and then place it into an AMS 2 Pro, which seems to seal better…..
I’ve gone through that thought process multiple times. If I wasn’t married I would have swapped out to AMS 2 Pro by now.
That said though I printed this (V2 AMS HT Desiccant/Silica Box - Variation 1 - Free 3D Print Model - MakerWorld) for it a couple of weeks back and it has transformed my opinion of the HT. The moisture gain is now similar to the AMS 2 Pro. Perhaps we have all been admiring the impact of lots of desiccant capacity in the AMS 2 Pro all along…
After taping up various components of the AMS-HT in stages and noting the RH for each area I taped, I can confirm that the issue is with the lid seal.
I’ve replaced every component through several rounds of warranty replacement with Bambu Support but nothing fixed the problem.
I was hoping after some time that someone may have figured out the best way to improve the lid seal as Bambu support don’t seem to have a solution. If anyone has progressed further than me I would love to hear from you.
Thanks for bringing that up, I would have had no idea.