2012 Intermittent Air Vent Issue

My 2012 Gen 3 Prius has been having an intermittent problem with the air vents. All of the modes either work just fine or do not work at all (defroster, air vents, foot vent, etc.). It's all or nothing. This happens randomly, but usually upon first starting the car after having been sitting for several hours (either throughout my work day or overnight). It has never just shut down if it was working while I am in the middle of a drive. I made an appointment with my local dealership, and of course the day of my appointment it is working just fine, so I just paid $155 for diagnostics only to be told they can’t duplicate the problem so they don’t know what to do or advise (very upsetting as I wasn’t told the problem had to be happening for diagnostics to figure it out, or else I would not have dropped it off knowing that it was working and having told them this up front). Any suggestions??? Thank you.

 

One day as I was leaving work the problem appeared again; nothing would blow out of any of the vents. So I drove it by my local Toyota dealership and asked the service tech to please come look at my car so that he could witness the problem and maybe have a suggestion for me. He gave somewhere under my glovebox a good "whack" and instantly air started blowing out of the vents again (I already had the air system turned on so he could see it should have been blowing air and wasn't). He said that was a very strong indication it was the blower motor and so I scheduled an appointment to have that replaced. After that appointment, everything has been operating as it should be and I have never had another problem with this, so clearly it was the blower motor. Also, they did gave me a discount on this work due to my complaint about the diagnostic charge I paid for basically nothing.