2003 Tahoe Heat. Help, my feet are freezing

2003 Tahoe with dual zone climate control.

I only get heated air out of the dash vents. Nothing comes out floorboard or defroster no matter what the mode control position. And, seemingly no matter what I set the temp on, the air cycles out of the dash vents from warm to cold and back constantly.

I have read about the blend door actuators frequently being the issue, but does it seem that they are the problem here? How many blend door actuators do I have, and is there any other sensor, etc, that could be bad? The fact that even set on 80 I get periods of cold air is puzzling.

I also notice that the temp control knobs are very "twitchy". Sometimes you can roll the temp up, the display will get to a certain point, then drop back a few degrees.

Any help or advice greatly appreciated

search here for "actuator"

very common and plenty of threads on it.

X2. But you may have 2 problems with the twitchy temp dial. If not the actuator it could be the dash controller failing intermittently or both. Did all this happen at once or at different times?

The dash controller has always been that way. The air only coming out of the dash vents happened suddenly.

If I have more than 1 blend door actuator, would it not be unlikely that both failed at the same time?

Thanks for your input and help.

do you hear any sort of clicking (like an actuator trying to move)?

there's a mode door that's similar to the blend doors - its located right above your right foot and it does the changing from floor to top vents to defrost.

i only had defrost and its because this actuator had stripped and would move the selection door to direct air to the lower ducts.

rebl68, you may have cracked the code. I bought this Tahoe with a lot of miles already on it, and did hear a clicking sound for a long time. I remember that I could stop it by turning the AC off momentarily, then back on. However, after a few minutes the clicking would start again. This was during warm weather when I was using the AC only. It may be that the actuator then failed (I eventually stopped hearing the clicking at all) before I needed to use heat from the floor vents or defrost, and when I did, the problem surfaced.

So, is it likely that its the mode door actuator that is bad, and not the blend door ones? If so, are there any tutorials around on how to replace it?

Many thanks for your help.

This thread's got a majority of the info regarding the various HVAC doors:
http://www.tahoeyukonforum.com/forum/showthread.php?t=15787

but this one will show you the mode door swap

http://www.sparkys-answers.com/2011/02/2003-chevrolet-silverado-changing-mode.html

you can reach it by hand if you can contort enough under the dash.

perhaps try cycling through the modes and reaching in to see if you can feel any clicking...

rebl68, can't tell you how much I appreciate your help.

Was just about to buy the wrong actuator from the local parts place, for $80.00 more, and they won't allow returns on electrical parts. I ordered the one from a link on the Sparky's thread you posted.

Many thanks again.

For future reference:

Blend door - controls mix of hot and cold air to the HVAC system by controlling flow of air past evaporator core and/or to the heater core.

Mode door - controls modes of HVAC operation. Defrost (upper dash), vents (ones in the dash pointing at you, and floor ducts.

Recirculation door - Controls air inlet for HVAC system between outside air intake (wiper cowl) and pulling air from inside the cabin.

There are actuators for each door.

Clicking noises behind the dash indicate the splined portion of the actuator that interfrences with the door stub is cracked, weakining the grip in the door stub, thus slipping and clicking on the splines.

Was hoping someone could help me clarify my issue. I am not sure if I need the mode door or driver side blend door. I do not have any issues with hot air blowing when i have the AC on.

My issue is that I get hot air from the defroster and vents, but the feet vents always blow cold air. I am leaning towards it being the mode door, but am not certain as air comes out of it, but it is cold.

Any clarification would be appreciated.