Heater issues

[Hafnuts]

I have a 2008 Sierra 1500 with heater control problems.  For several years it would produce very little heat.  My local mechanic would "recalibrate" the control and it would work fine for a few months.  Last year instead of working for a few months it would only work a 2 to 3 weeks.  My mechanic suggested that I take it to a dealer to diagnose a more permanent  solution.  The dealer said that the recommended fix was to again recalibrate which they did but it is again not working.  They said if the calibration failed again that the problem might be the HVAC controls or the heater door actuator but since they had never seen this problem before were not sure if either was the actual problem.  Any suggestions for a permanent fix? 

[davester]

I would first check that both hoses to the heater core get hot with the engine (ie, that water is flowing through them).

Then I'd take off the actuator for the blend door and see that it moves appropriately as the temp control is moved, and that, if possible, it feels like the door actually moves with the post that goes into the actuator, and that the post isn't rounded off.

 

Finally, I would not return to a mechanic that said he had never seen an blend door actuator problem i a GM truck.  It's a pretty common thing to fail.