My AES Chamber is not reaching the desired Humidity (RH) set point.

This FAQ Troubleshooting Guide refers to chambers built after 2008 with an F4T controller. Please contact technical support if your chamber is an older model. All corresponding images are linked and are listed at the end of the article.


WARNING: RISK OF ELECTRIC SHOCK AND BURNS. Only qualified personnel should perform any repairs to your AES chamber.  Please make sure that the chamber is turned off and unplugged before performing any maintenance or repairs.

Step 1: Water Supply

There are a few simple things to check after ensuring proper water supply and referencing the Humidity Range Chart to make sure you are within the chambers capable temperature and humidity ranges. 


What is my correct PSI of the water input? 

Please refer to the back of the chamber to establish PSI input. (If you have an external tank, please ensure this is filled during chamber use). The PSI input is located on a sticker next to the humidity system water connection. Also, verify all water related valves are open and connected to the right ports.


What type of water should I use in my test chamber??

AES' environmental test chambers use single distilled or demineralized water. For more information on what kind of water should be used take a look at What kind of water should I use in my AES test chamber”.


Step 2: Controller (F4T)

What can I check on the controller to see if my humidity is working correctly?

Start with checking to see if the humidity control loop is set to AUTO, you can find this to the right of the humidity header bar. There are three selections to choose from, AUTO, MANUAL, and OFF, AUTO should be selected here.


My control loop is set to AUTO and I still have no humidity control.

You will then need to check to see if there is a request for humidity on the controller.

There are two progress bars at the bottom of each control loop. The humidity control loop will have a percentage bar for humidity as well as a percentage bar for dehumidification. If the controller is requesting the humidity to be raised, the upper progress bar will show a power request in percentage required to get to the requested setpoint. 


Step 3: Electrical Circuit 


I’ve completed the steps above and the chamber is still not reaching the required set point. 

If there appears to be a request for humidity coming from the controller, the next area to check would be the thermal safety switch on the steam generator itself. This can be accessed by removing the side access panel after powering off the chamber and locating the automatic reset switch located on the steam generator.  

Remove any product and test fixturing from the chamber working volume and set the chamber controller to the desired setpoint.  The chamber may take up to an hour to stabilize at the desired humidity setpoint.

Please refer to the Troubleshooting AES Humidity Chambers for step-by-step video instructions. 


I have reset the steam generator, and powered on the machine; I am still not getting humidity in the chamber. 

It looks like you might need a replacement part(s) or service. Please follow the instructions below, document your findings and call support. AES will be able to assist you better in diagnosing the problem.

When looking at the PCB board please check the following. The chamber needs to be on and running, so please use caution and please do not touch any of the elements.

  • Check the humidity breaker on the PCB, make sure that the light is on and it is set to “reset”
  • Find the F2 Fuse and make sure it is not blown. DO NOT TOUCH AS THIS IS LIVE.
  • Check the stage light to see if this is on (picture included below)

If the steps above do not work or you have an older chamber, please reach out to support: or call 978-772-0022



Humidity Range Chart



Steam Generator Reset


PCB - NOTE: Components on board might vary depending on chamber model.