Is my Air Conditioner creating humidity in the room?

[humiditycrisis]

I am hoping you can help me solve my problem. I need an air conditioner for a room where I keep some old collectible items that are very sensitive to both temperature and humidity. I've had three air conditioners installed in this room all from the Haier brand, all 9000BTU.

The first one was a model from the early 2000s. I used it for 12 years until 2012 when it stopped working and I had to replace it. It served the purpose well since besides lowering the temperature to around 22C (72F), it also did a good job in lowering the humidity from the room's typical 60% to around 35% (when set to dehumidifier mode with fan set to a minimum).

The next one I installed however not only didn't lower the humidity but actually increased it to around 75% when turned on, set to dehumidifier mode with fan set to a minimum. With other setups the humidity increases to as much as 90%! I called several expert technicians asking them to check out what's wrong but none have been able to solve the issue. I even replaced the air conditioner with a new one thinking it was faulty but even that didn't help.

The humidity caused much damage to my collection and now that I am getting some new expensive pieces I really need to solve this issue badly. If anyone here could enlighten me as to what may be wrong and what I can do to solve the issue I would be very grateful.

Thanks

[Sergroum]

Hmmm. Needless to say air conditioners usually remove humidity, not add it.  Sometimes there are cases where the AC is satisfied and stops working, but fan continues going even while the coil is still moist. This reintroduces the moisture it pulled out from the air earlier.  But it would be at worst, a net Zero in my head. The moisture needs to be coming from somewhere.  Somewhere else.

Is the location you store your collectables in sealed? From the rest of the house? Open/leaky windows?

[Hvacpimp]

Sergroum is right about the continuous fan increasing humidity. Also, the unit might be oversized which might cool the room but not dehumidify properly. Fan speed set too high? Open/leaky window as mentioned before?