Drivers or passengers side of the vents are not working for AC or heater?

Turned out it was the top one.

Hello, was having same issue on driver side. 04 silverado, 5.3l V8, Crew Cab, 4WD. I have dual climate control with digital display. I can confirm that the actuator located above passenger side floor board, near front of center console, does serve the driver side vents. My issue was intermittent, sometimes would work fine, but most the times it would start acting up 5 or 10 minutes down the road. Would blow cold air out of both sides, then all the sudden would start blowing hot air out the driver side. Turning truck off and back on would usually fix it, but again for only 5 or ten minutes. I was able to repair my actuator.
Found actuator and removed. Then opened it up to expose the guts. Small motor, 4 gears, and circuit board. I removed the black gear by lifting straight up, noticed attached tonthe gear were 2 metal tabs which touched the circuit board. This is what provides position feedback to hvac system to let it know the position of the damper actuator. Noticed on the circuit board where the 2 metal rabs ride, there was a bunch of grease built up on the track. Grease is what lubricates the plastic gears. Proceeded to clean the grease off. Reassembled and reinstalled actuator. Voila. So far so good.

Passenger side putting out hot air? One side is working?

Okay, I found two the bottom one is working the top one is not. The one you cannot get to of course that requires the whole dash to be removed (right).

My finger is pointing to it in one picture I replaced.

For several years cool one side not the other. Then reverse happens. Then works fine for weeks. Now no heat from any side of defroster. Just blows cold air.
Any ideas?
Thanks

I believe I have an auto system. I can pick a temperature and it will adjust and maintain
the selected temperature. I do have a dual climate system. At the moment I have no heat from either side, nor from the defrost position, no matter what the selected temperature is. Blower works fine, I just replaced the blower module with in the last month.
Thanks for your help.

Thank you I will give it a try.

Well, yesterday morning truck overheated. Changed the thermostat, solved that part. Did as directed. With truck hot, heater on high, only one hose hot, other cool. Slight amount of warm air blowing. Wonder if the radiator needs to be boiled out. Seems that there is a slight leak at the fitting through firewall on the hot side. What do you think of this idea?

Driverside vents will blow hot air while passenger vents blow cool air while using the air conditionre. Problem is corrected by shutting off the engine and restarting. But problem reoccurs. Could this be a blend door accuator issue and if so which one? Thanks

Thanks! I will try this.