2009 Hyundai Sonata - heater only blows warm on passenger side?

I am sure it is nothing you are doing. Please look with a flashling into the air outlets and see if there are any obstructions on the driver's side. Heater outlets are under the dash near your feet. Change the direction of the air(most cars you can direct them to vents or the windshield) and see if all other air outlets are working OK. If so I would suggest a call to your dealer's shop and ask them if they have any recalls or know about similar issues with your car year and model. There are doors or valves that move the air to the selected outlets and the one towards the driver's foot well area may be stuck closed. In any case this needs a professional mechanic's touch. Check the warranty. Hyundai vehicles have excellent coverage and this could be still under warranty terms. Sorry about your troubles and good luck.

I am sure it is me!!! I just bought the car in April and this is the first time ive had to use the heat, my manual shows heaters with knobs that turn, i dont have that set up!!! I will try what you recommended. Im pretty sure it is just a matter of me not knowing how to work it!! Thanks!

being a limited edition sonata im assuming that it has dual climate zonesfor the drivers and passenger side of vehicle. the temp door actuator is probably bad on the drivers side. if your under 60,000 miles its covered under factory warranty. if your over 60 k its actually quite easy to change.

One more thought: does your car have individual zone controls? My 08 Mercury does and the driver and the passenger can adjust their own temperatures. If so your controls needs to be adjusted or even turned ON to control the temperature on the driver's side. The owner's manual has all the instructions you should need to operate the AC/heat properly. Sorry, just thought of this today. Good luck.