Help: HVAC Only Blows Out Defrost & Feet

[SmokeShow]

I couldn’t find a more appropriate sub-forum to post this but mods move this wherever it belongs or will get the most exposure if this ain’t the right spot.

Anyway, as the title says, on my wife’s 2002 2500hd LS d/a the HVAC is now only blowing out of the defrost and feet regardless of which mode it’s switched to. Internet search says this can be a number of things - a blown fuse, bad resistor/relay somewhere underdash/glovebox, blend door broken (take dash out ugh) or mode actuator bad ($65-95 part near throttle pedal - think it’s what moves the blend doors) or some hvac control module recalibration via a hokey pokey dance with key & controls (this may have been for 03+ systems?)? I know most of those are probably a PITA to change.

I’m hoping for a couple pieces of info. 1) any ideas which one it may actually be or other ideas as to what it could be? 2) anyway I can troubleshoot any of those prior to tearing things apart - I don’t want to waste anymore time or money on things than I have to only to have it still not work right after changing something. Ugh

Any insight would be appreciated.

 

[clrussell]

Mode door acuator.

 

[duramax on fire]

Yep blend door. Drivers side under dash. Use flash light it'll have a 4" oval type arm on it. Or half circle looking Change modes and see if it moves. Little tricky to change out but not bad. Get a gm replacement

 

[SmokeShow]

Thanks guys. I’ll check it out tmrw.

GM Parts Direct...ac Delco... is that the place to get it or somewhere else? It’s over $100 on there with shipping. Google search found the same part number elsewhere for $65+shipping.

 

[2004LB7]

Before you get too deep into it, try rebooting the HVAC module.

Pull the HVAC fuse and leave it out for a minute or two. Put it in and start the truck. Let it idle. Dont tuch the ac controls for at least a minute. You may hear the blend doors moving. If all is good you may not need to tear into it at all

 

[SmokeShow]

Before you get too deep into it, try rebooting the HVAC module.

Pull the HVAC fuse and leave it out for a minute or two. Put it in and start the truck. Let it idle. Dont tuch the ac controls for at least a minute. You may hear the blend doors moving. If all is good you may not need to tear into it at all

Sounds good. I’ll do that!

Is that fuse in the panel on the driver side of the dash or under the hood?

 

[2004LB7]

Under hood if I'm not mistaken

 

[melms23]

Underhood. I had to do it to my old LLY once after it sat a while without batteries in it.

 

[1FastBrick]

Given the age, it's likely the motor finally crapped out.

 

[SmokeShow]

Not surprised but the fuse reset thing-a-ma-jig didn’t fix it. Guess I’ll order an actuator.

 

[Chevy1925]

Not surprised but the fuse reset thing-a-ma-jig didn’t fix it. Guess I’ll order an actuator.

Yeah, doesn’t work on our years.

My truck won’t change from recycle to outside air nor wil it change from vents to anything else. I tried an actuator on the recirc/outside air door and it lasted about 2 months. Not looking forward to taking the dash apart to fix it. Maybe next winter and I’ll do a heater core with it for shits and giggles

 

[SmokeShow]

Yeah, doesn’t work on our years.

My truck won’t change from recycle to outside air nor wil it change from vents to anything else. I tried an actuator on the recirc/outside air door and it lasted about 2 months. Not looking forward to taking the dash apart to fix it. Maybe next winter and I’ll do a heater core with it for shits and giggles

What do you think is wrong with yours? Broken door in the system somehwhere?

 

[Chevy1925]

What do you think is wrong with yours? Broken door in the system somehwhere?

I don’t know honestly. I almost think it’s electrical but I’ve tried changing the head unit thinking that might have been it, wasn’t. I’m assuming either bad actuators again or broke blend door/s. The recirc door has a mind of its own. It will change on its own randomly too. Tom sent me bunch of actuators and electrical harness for me to swap in if I find it’s one of those

 

[THEFERMANATOR]

Alot of times the actuator isn't bad. There is a resistor strip inside that sends back actual position info of where the motor actually is so it knows. GM used white lithium grease in these actuatos stock, and overtime the grease hardens and blocks the sensor from sending position value. When this happens it defaults to full open and stays. This is what causes the infamous hot on one side and cold on the other. I replaced a few, but found in 10 minutes I could pull them apart, spray em out with electrical cleaner, lube it with electrical contact grease, put it back together, and they worked like new again.

 

[Chevy1925]

Alot of times the actuator isn't bad. There is a resistor strip inside that sends back actual position info of where the motor actually is so it knows. GM used white lithium grease in these actuatos stock, and overtime the grease hardens and blocks the sensor from sending position value. When this happens it defaults to full open and stays. This is what causes the infamous hot on one side and cold on the other. I replaced a few, but found in 10 minutes I could pull them apart, spray em out with electrical cleaner, lube it with electrical contact grease, put it back together, and they worked like new again.

Good to know ferm! Sounds exactly like my issue. I’m sure AZ heat affects this well

 

[SmokeShow]

Likewise, thanks Ferm. Maybe I'll pull the thing out and "service" it before buying a new one. We are talking about the actuator on the driver side right above the throttle pedal, right? Looks like this...

 

[Chevy1925]

Likewise, thanks Ferm. Maybe I'll pull the thing out and "service" it before buying a new one. We are talking about the actuator on the driver side right above the throttle pedal, right? Looks like this...

i think they are all the same but its been a while. so that by the throttle pedal is for the vents,defrost,floor blend door? might pull that one here soon if its easy to get to. have not looked yet. I got to the recric/outside air one without pulling the dash but it was a royal pain to fit my hands back there.

 

[SmokeShow]

I didn't decipher how it comes out of there yet, but yeah, it's right above the throttle pedal. There is a big dash support brace right there too. And as I understand it, that thing's actual name is "mode actuator". Switches modes - i.e. floor, floor&dash, dash, defrost.