Air only blows from defoster vents

[notbob]

2001 GMC 1500 SL 5.3.

 

I know this is common but not sure how to diagnose it. Need to get back to cabin vents or floor....until it rains and gets cool and I will want my defrost. .. you get it.

[00Silverado4x4]

Sounds like the mode actuator has gone bad. It's located up under the driver side dash above the gas pedal area. There are videos on Youtube that make it look pretty easy.

[notbob]

Thank you

[desrtrat]

you can try shutting the h-vac switch to off, and disconnect the negative cable for a minute or two. sometimes the BCM will get a brain fart and not control things properly. if not, see above..

 

good luck

[steveo77]

My experience is that both above are good advise. The part is called the mode level actuator...