HVAC dial doesn't work until truck warmed up

[Dadwagon]

My HVAC dial will continue to move the temperature lower despite spinning the knob in either direction. The temperature doesn't change on it's own, it goes to lower temperature as the knob is moved. This happens when the truck is first started, and goes back to "normal" operation a few minutes later when the 4.2 is warmed up. The HVAC system heats and cools just fine, and I have a dead actuator that doesn't let me move air to the head/upper section. Is this a sign the connector in the back is loose, or do our trucks seem to do this as they age? 140k miles.

 

[Mooseman]

Is it an auto digital HVAC system? Even when cold, if you crank it up to max heat, it would stay there however, when set to auto, it would wait until the engine has started warming up a bit before turning up the fan.

So you turn it up and the display won't stay there? Or do you mean that you crank it up and the display, a few seconds later, shows a lower temp? That is normal. it automatically reverts to showing the outside temperature.

 

[TJBaker57]

I would have to check mine to be sure of this.... But I have some weird behaviour with mine also. Automatuc controls with the steering wheel controls for temp and blower also. Sometimes when I turn my drivers side temp upwards to hotter using the knob the setting in the display goes down instead of up. So I use the steering wheel control instead when this happens

 

[Dadwagon]

It has the dual-zone HVAC with an auto setting, with a rear seat blower.

I turn the vehicle on in the morning. I can turn the fan speed up and down as normal. The knob that changes the temperature up and down is what is screwy: Turning the knob left or right either doesn't cause the temperature to change, like it skipped, or the temperature goes up (warmer temperature) by a degree but then immediately jumps down. Or it just bumps down (colder) with any twist of the knob. TJ Baker is experiencing the same thing: using the knob the setting in the display goes down instead of up.

After the car has been run a couple of minutes, the knob goes back to normal and can be moved in gentle increments of one degree at a time or spun a bit more quickly. It's almost like the truck is saying, "nope it's too cold for that temperature" and refuses. Hidden feature? ha ha

I don't have HVAC controls on my steering wheel.

 

[Mooseman]

Sounds like the button is either worn or dirty. You could try pulling the knob and shooting some contact cleaner into the button's shaft. Failing that, I'd just replace the whole thing from a junker. Just be sure you get one from the same generation truck as there was a change in the A/C on/off display. Early versions had a "A/C off" message whereas later ones have a snowflake that comes on when A/C is on.

 

[Reprise]

I can turn the fan speed up and down as normal. The knob that changes the temperature up and down is what is screwy: Turning the knob left or right either doesn't cause the temperature to change, like it skipped, or the temperature goes up (warmer temperature) by a degree but then immediately jumps down. Or it just bumps down (colder) with any twist of the knob. TJ Baker is experiencing the same thing: using the knob the setting in the display goes down instead of up.

This is not a feature; it's a bug. I have the same thing with mine.
Like @TJBaker57, I have the HVAC temp / fan controls on the upper LH side of the wheel, and have gotten in the habit of using the steering wheel control (SWC) for temp changes.
He and I have the only two years where the HVAC controls were on the wheel. Starting in '04, that area got changed over to OnStar functions. But you don't have SWC at all, so it's kinda immaterial for you, anyway.

If you stick with the dial on the control head, it will 'wake up' and start moving the correct way when you turn it higher or lower. But every time you first touch it, the temp display will move in the opposite direction from where you first turned it. Since I have the SWC, I just got in the habit of changing the temp from there, as it always works properly from that location.

For you, if you didn't want to deal with this, a used control head would potentially fix this for you, but you'll need to be careful, as some of the control heads don't work properly with some MY (I think at least one breakpoint is the early '03-'04, vs. the '05-up -- there's a lot of little things that got changed between '04-'05). I kind of think of that point as a 'mid-model change', or MMC, even though nothing on the exterior really changed (front / rear fascia, etc.)

I mention 'used', not just because it's cheaper, but also because I think it's one of those parts that needs to be added to the communication bus, if it's brand new (via a Tech2), just like a door switch module.

Somewhere on this site, there's a post that talks about control head compatibility by MY, IIRC. If it's not here, it might be on the 'old' site. But I think it's here.