2005 Chevy Impala - Driver Side Heat Not Functioning

Hello all -

I drive a 2005 Chevy Impala, and last year around this time I noticed that the driver side heat was not functioning. I sucked it up for a couple of weeks, and then one day it kicked in and I experienced no problems during the remaining winter months. Fast forward to this year, and I have encountered the same issue. I have the heat cranked all the way up for both the driver and passenger side, however heat only comes out of the passenger side. I keep hoping that it will magically work again, like it did last year, but I would rather just end this problem once and for all.

Thanks for the help!