Ive read several of the current posts and some random google searches and not sure if this is linked to the other issues Ive read. 2000 silverado SL package. In ...

Ive read several of the current posts and some random google searches and not sure if this is linked to the other issues Ive read. 2000 silverado SL package. In short....when the rotary temp knob is set to hot, cold air comes out or for A/C ops, and when it set to cold, the air is hot or the heater works. A Vac line reversed somewhere maybe?
Thanks in advance.

Has there been any work done in the past to the heat actuator?

Not that were aware of. We bought the truck a few weeks ago used and the seller said nothing about repairs. Awful lot of gizmos relate to the heat and cool system it seems.

Electric air blend motors are used to direct the air through the HVAC system. They are mounted on the driver and passenger side of the HVAC plenum. (you'll need a manual to verify which is what)

One of these motor assembly's was probable changed out and the incorrect P/N was used to control the main internal door that directs the heat/AC.

I have had this happen to a Buick I owned. The motor was bad, the shop ordered the incorrect p/n and installed it. It fit but operated in reverse of what it should have done. They corrected the problem. But on that car there were, IIRC, 6 different units installed on the plenum.

Sounds like the culprit. But geezzz..I looked up on a on line supplier and there are like 10 or more different motors from each of several suppliers. Guess I need to yank it and see if it has any GM numbers on it. Thank You RivGuy.

Are you sure it has the right dial face on it?