The hair collection chamber is the area underneath your trimming attachment, where all the hair get sucked in. Once this chamber is full, it will no longer have the capacity to hold any more hair. Then it may seem like the vacuum system is not working. However, you just need to empty the hair chamber.
Open the hair collection chamber and shake out all the hair collected in it. Use the brush supplied with your trimmer or a cotton bud to clean any remaining hair still stuck inside the chamber.
If you have a very long or dense beard, the hair chamber will fill out quicker. In this case, you may need to empty it during the trimming session to make sure the vacuum functions properly.
Never use water to clean the hair chamber as this can damage the appliance.