Hello,


Thanks for taking some time to read this. New to the forum but long time technician. Wife has a 2003 Suburban 2WD LT with Auto HVAC. Upon purchasing the vehicle three years ago, the heat would only work on 90(Max). If you clicked it one degree lower, it would send out 65 degree air. I checked the Driver'* side blend door actuator, and also replaced with a new Delco unit with no repair. Internals of HVAC actuator did show some damage to plastic gears, so this was not a total loss, but I did learn it was a control issue after. Next, while watching HVAC sensor data on the scan tool, I noticed the internal temp sensor (located right above drivers seat in the ceiling) increased in temperature very quickly while actual temp stayed the same. As soon as the temp readout on this PID on the scanner showed 88-90 degrees F, the air would begin coming out cold again while the temp on the control head was at 89 or lower. It was a cold night, so I disengaged the sensor from the ceiling and placed it outside of the door while testing. Boom, problem fixed. But, and this is where the frustration starts. New Delco internal air temp sensor, issue fixed for three-five key cycles after recalibration HVAC system. Next I replaced the original HVAC Auto control head with a new Dorman (yes, their quality sucks, and I'm not paying $345 for a new Delco unit). Recalibrate AGAIN, and again, 3-5 key cycles the heat works great anywhere from 80-90 degrees with very little change as it should be in this range. Then, it happens again where the setting of 89 starts to blow out cold air. So, in short, a new Head, Drivers Blend Door Actuator, and internal temp sensor have not fixed my issue. Lost on this one guys, even a former GM tech is stumped. Vehicle also has a rear HVAC internal air temp sensor above the 3rd row seat in the ceiling as well. Fan inside is noisy, but I do not believe there is a PID for this sensor under the HVAC or Rear HVAC settings in the Snap On, so no current place to confirm. But if it'* bad, why would a rear sensor cause this? May not be related. Anyways, GM guys and gals if you have something for me to test and inspect, I'd love to hear it.. Thanks for your time

TomInNC

Welcome aboard,
If you would like to contribute we can always use another tech'* experience.
Program it again and see if that'* what'* happening. I've seen weird issues with loss of programming. Seen a couple that lost programming and never did find out why.