Hvac only have hot air on defrost. 2000 blazer

[chevy1955]

Heater works but only when on defrost. It is the auto a/c controller and I installed new ac Delco but same trouble. Every other function works. Any info would be great.

[stevenof9]

I have a 2000 Jimmy (112,000km!) and I had a vacuum leak that affected the HVAC dampers and 2wd-4wd electronic shift (the actuator is under the battery). Fixed the leak also fixed the hvac issues.