Intermittent front vents

Occasionally the front vents will be nice and blow hot/cold air. Unfortunately, they are unreliable and choose not to work most of the time. I read about some kind of technique to fix something like this on a 9-3; take off dash and drill some screws?? I'm not sure if that applies to me so i'm looking for some help. It isn't showing any codes of malfunction and it seems to work more often if I press the recirculating air button. Other than that, I pretty much have a useless AC system as my feet and windshield are getting all the air. I've been relying on open windows and my vented seats all summer and I'm starting to get pissed.