HVAC only comes out windshield

[eliminatethebug]

My blower only sends air up to the windshield. Is there a vacuum line on this truck that is disconnected? On my previous 03 F150 when it did that the vacuum line to the HVAC head was split.

99 Yukon SLE, 5.7L V8.

 

[Doubeleive]

most likely it is a electrical actuator, the one that controls defrost, not sure when gm used vacuum line for hvac control or if they ever did, they used to be cable controlled, never seen one that is vacuum, the only thing on a gm that I have seen vaccum controlled was cruise control waaay back.

 

[eliminatethebug]

Thanks.

 

[YukonGTmaster]

Look under your dash from the drivers side. With the key on and the fan speed on low, rotate the mode knob through the different positions (Defrost, Floor, Center etc.) You should see the Mode/Blend door actuator moving. I had a similar problem where the actuator broke, and there were arms just dangling. The actuators don’t cost much if I recall.

 

[exp500]

Look on the firewall under hood above heater core. Small -1/8-3/32 vac hose about 2 feet long.

 

[Eman85]

No vacum on a 99 except for the heater control valve in the heater hose. As other said look up near the gas pedal on the side of the heater module for the actuator. Is your dash cracking at the defroster vents? I've seen piece of that break off and jam the door.

 

[eliminatethebug]

Thanks. No visible dash cracks that I've noticed. I will look under the dash at the actuator, I found a YouTube video that shows the location.

 

[east302]

The notched silver dial on the actuator doubles as a position indicator as the dampers rotate. See if it matches the photos below. It should turn smoothly as the dial setting is turned, no jerking back and forth or rhythmic ratcheting sounds. Compare the linkages as well to make sure they’re intact.