Is there a troubleshooting methodology for a 2001 Tahoe heater issues. Heat works on upper setting. if you change to defrost/heater it blows cold air. if you change to lower setting, it changes to outside air only and will not change back to recirculating. I would prefer to go through a troubleshooting routine rather than R&R parts till it works correctly. Any suggestions would be appreciated. thanks in advance

 

Welcome to the forum.

 

Welcome to Chevy Missing! Lot of smart folks here will help you with your problem, stay tuned. These heater/ac posts are a common complaint.
I got nothing for you - I'm a veterinarian, not a mechanic!

 

Thank you, appreciate the group.

 

Disclaimer: My hands-on experience comes from a 1994 and a 2005. There are electrically-actuated flaps/"doors" in the vent system under the dash; my 2005 had three of these. These direct the air flow to outside/recirculate, to windshield (defrost) or heat underneath the dash or to vent right at the driver and passenger. The third one may be for driver/passenger split. Oftentimes when these go bad one will hear a clicking from stripped gears.

For our 1994 I paid the shop $400 to replace one (which fixed it), for the 2005 I replaced one actuator with an aftermarket Dorman part. In the 2005 I could hear/feel which actuator was bad after removing the bottom panel with a 5.5mm shortened socket, and I unplugged the harness and turned the actuator with a screwdriver, and drove it like that for months. Then I replaced it, was easier than getting the bottom panel off !!!

One thing to try: disconnect a battery cable for 30 minutes to re-set the computer, then try.

 

Recirc is not allowed on certain settings. It's so humid, moist air is driven out of the cabin to help clear windows.