Its a 99 with manual controls all of the vents will change but it blows hot like the heater is stuck on.
Iv searched but cant seem to find anything.

 

Do any of the ***** respond? if you try to change from Face to floor or to dash does it change?
If not the unit could be froze up? Unplug it from the dash and plug it back in to see if it clears up.
Others will chime in with other options

 

Ya it changed from face to defrost to floor just not hot to cold.

 

I had a missing belt that kept the ac from getting cold. check that.

 

Ya u have a separte belt just for the a/c but it should still blow some what cool even with the belt off! maybe u have a vacume problem n the dash!

 

Oh hell how would i find that?

 

These systems are electronic, no vacuum controls any more Have someone switch from hot to cold and observe the temp mode blend door actuator to make sure that it moves, if it does not it may be smoked. Also, does the ac compressor kick on when you depress the ac button? Maybe everything's working but there's no R-134a in the system?

 

I'd bet its those blend actuator motor things. Mine were freaking out there for a while but eventually stopped acting up.

 

It's either the actuator or the control head. Very easy to swap a control head from a buddy's truck before you buy a part.

 

My Sierra done that too me in October on a hot *** day, but it's been fine ever since.