2009 silverado ltz

hi my 2009 silverado ltz is haveing heating issues. when you first start truck all work fine. after a couple min the drivers side vents loose heat and blows cold air. the heat on the pass side works fine. then the vent will change to defrost even though the display still shows its on vent. the only way to get it back is to mess with the vent control. then it will last about a min then back to defrost. at this point i just turn it off.i have already replaced the control panel to no avail if anybody could give somewhere to look it would be great. thanks

hi my 2009 silverado ltz is haveing heating issues. when you first start truck all work fine. after a couple min the drivers side vents loose heat and blows cold air. the heat on the pass side works fine. then the vent will change to defrost even though the display still shows its on vent. the only way to get it back is to mess with the vent control. then it will last about a min then back to defrost. at this point i just turn it off.i have already replaced the control panel to no avail if anybody could give somewhere to look it would be great. thanks

You need to get it on a good good HAVC capable scanner and check for codes and mod door operation.
Lot of mod door motor operations.
Post back any HAVC codes.