My buddy has 99 1500 4x4 with the 360. Recently the air is just randomly switching between blowing hot and cold air. It blows hot more of the time then cold. When the air does turn to cold, it feels good. I checked check valves and no luck. I have no clue what this could be. NEED HELP ASAP. Its hot as hell outside and having no air sucks.

 

Does the 99 have the little servo motor for the temp door? (it's either electrical, or cable activated) Look under the dash, just to the right of the trans tunnel. If you see a little square box there, with an electrical connector, you have the servo motor, and need to check out heatertreater.

 

Check the tiny plastic vacuum tubing from intake through firewall. A leak (these lines are prone to breaking) .

 

Temp door is not vacuum controlled on any of them. (or, blend door... for the technically accurate term. )

 

That's right......mind is fuzzy. I had a short tem issue when I di my kegger and broke a line. Think it was the wild vent thing.