mine does the same thing, i have the digital controls though... my money would be on the blend door actuator like budhayes said. i have a feeling thats what my problem is too and its a fairly common thing from what ive gathered

 

Where is this? how do i check it?

 

 

K found it, it seems thats it wont let itself open for some reason like it needs to be calibrated or something. when you put it to heat it trys to turn even tho its already open to the max. when you turn it to cold it only moves a little then stops.

 

.....

 

mine has a problem where if i turn max heat on, i cant turn it off. if i let the truck sit for a few hours, and then get back in, it will work normal as long as i dont go max heat, or it sticks there again.

 

everytime i reset computer form disconnecting batt it does this. i just turn it off and on then go for a drive with it off then turn it on and its fine. scared me first time lol. i have digital controls too.

 

I have manually controls the gm tech said the 99s dont reset.

 

The actuators need to be calibrated with a Tech 2 scan tool. They need to relearn their positions otherwise they are erratic. It is a simple 3 minute procedure. Most shops charge 1 hour labor.

 

a hour labor for a 30$ part?