You have a set of electronic mode motors on the climate control module under the dash the one that controls the drivers side has most likely failed. You can try unhooking the batt. for a minute and then hook it back up this will rehome the climate control mode motors and may get it working again otherwise it will have to be replaced.

This will let you know how to replace drivers side or the passenger side actuator. Passenger side difference is noted at end of this letter. My 2004 Chevy Impala driver side climate control was stuck on cold, no matter where I switched it to. The light on the panel was also out. Resetting by disconnecting the battery did not work. I had to buy and replace the drivers side actuator (Part Number 15844096 - $38.46 at Chevy dealer). The passenger side actuator is also the exact same part number. They are both located under the dash, about equal height as the climate control knobs. Make sure you disconnect the positive cable on the battery before removing the switch. Drivers side actuator is accessed by removing the bottom dash cover on the drivers side. Two easy clips to disconnect the dash cover, remove the floor courtesy light by twisting, and the cover comes right out. The drivers side actuator is harder to work on than the passenger side, due to room. But I replaced my actuator with only having to take off the bottom dash cover. There are two screws holding the actuator on. I used a 1/4 hand driver with a 3" extension, a 1/4 universal joint for the 1/4 socket (and the universal is needed), and a 7/32" socket. These were the only tools I needed. After unscrewing the two screws, I pulled the actuator off of a small arm it is connected to which switches the flap for the climate control system between hot or cold. I then was able to let it hang down, and disconnected the wire running to the actuator. Room was an issue, and I did some of this by feel. Now comes the tricky part. The new actuator has to slide back on the small arm, but it is flat on two sides, with rounded ends. The new actuator has to match the flat ends to the same position as the old actuator. I hooked the wire onto the new actuator, and let it hang down. I held the old actuator up by it, and had my wife hold the battery connector to the battery to get power. The new actuator will rotate when the connection is made, and stopped rotating when I had my wife pull the connector from the battery. It took a couple tries, but I finally got it to stop at the same position as the old actuator. I then lined up the new switch, and got it on the control arm. This took a few minutes and tries, as I had to do it by feel. I then put the two screws back in and tightened them down. Again, tricky due to room. Once done, I put the cover back on, reconnected battery, and warmed up the car. Was very happy to find that I now had heat on the drivers side, as Michigan weather is cold this time of year. One note is that even though I now had heat, the light on my drivers side control stayed out. I can live with that though. The whole job took me about an hour and a half. Also, note if you have to replace the passenger side actuator, you need to remove the passenger side bottom cover on the dash. You then remove the glove compartment door by removing the five screws on the bottom of the door. Slide the whole glove compartment door out of the car. You will be happy to know you have much more room to replace the passenger side actuator, so it should be much easier and quicker than the drivers side.

doitmyselfer, I want to thank you for posting the instructions and problem you had with your impala. I had the same problem and googled it and came across your post. I brought one online and installed it myself using your instructions. I used a deep socket and got straight onto the bolts and had to use 12Vs from the battery charger to rotate the actuator to get it to line up. Works like a champ now! again thanks for saving me at least 175 bucks. Rc....