Need some advice

[toddwarren]

I know this will show my ignorance, but what is the matter with the truck when the A/C blows normal then under a bit of accleration goes through the defrost vent?? Mine just started this and I hate it.

How about the doors used to lock when put in gear and now all the sudden lock randomly minutes later after being in gear?

Thanks!!!!

[SILVER2000SVT]

Under a loss of vacuum the system is designed to default to the defrost position.
The HVAC damper position is controled by engine vacuum. Sounds like you have a vaccum leak somewhere. The leak could be anywhere but the specific line that controls the HVAC controls enters the cab in the area underneath surfboard on the dash. Also, There is a vacuum resevoir beside the battery box that is supposed to aid in keeping a constant vacuum to those controls inside the cab.
Has anybody been messing with the vacuum lines (aftermarket boost gauge, cold air intake, etc). You could have the cabin vacuum line hooked up to intake manifold which would go positive during acceleration.

I thought the doors lock once you are in motion? I don't ever remember the doors locking immediately when you put it in drive. That's more of a GM thing from my experience.