03 Yukon Auto-Climate Control Blower Strangeness

katiedawg · January 13, 2014

Haven't seen this one in all the searches - sorry if I missed it and posted about something that's already been answered.

I've seen plenty of posts about the auto-climate control actuators acting up and causing hot air from the console vents or cold air from the floor vents or the system stuck with only the defogger vents working, but this is different.

I'm driving down the road with the system set on Auto and notice it's slowly getting colder in the truck. OK, I'll bump it up a couple of degrees. Still cold. I reach under the dash and nothing's coming out of the vents. Hmmm...so I ran the blower up all the way and it ramped right up, but there was no output from *any* of the vents - floor, console or windshield.

I'll skip all the stuff I tried (and I tried lots of stuff in a hurry - it was 12 degrees outside). I still had the blower running wide open with no output. When I pushed the defrost/defog button, the windshield vents slowly came alive and I had tons of heat blasting away. Great - I put it back on Auto and it started behaving just fine. I chalked it up to the extreme cold.

But it comes and goes now. Mostly it behaves, but every now and then it will block the blower output and I have to run the blower up all the way, put it on defrost/defog, wait for the heat to blast out up top and I'm back in business.

I've read about the auto-cal the system performs after a battery pull, but my battery was replaced about a year ago and the techs told me they'd let the system sit and calibrate itself before driving it out and handing it over. (I didn't know what the heck they were talking about, but I do now.) Also, I'm the original owner, and I know nothing's been modified or tinkered with on the vehicle.

So does this still sound like an actuator issue? If so, which one? I'm pretty handy with smaller stuff (I used to tune up my 65 Mustang - easy to do back then). Or is this a trip to a local mechanic or even the dealer?

Sorry about writing a book - I just want to be clear on the symptoms and what I've tried.

Many thanks in advance...

katiedawg · January 15, 2014

Gee, don't everybody answer all at once...

Seriously, no ideas? Too many smart folks hang out here for this to get no comments.

txab · January 15, 2014

You might try the HVAC recalibration.

Remove the HVAC/ECAS fuse for a minimum of 10 seconds.

Re-install the HVAC/ECAS fuse

Turn key on, but do not start. Make no adjustments to HVAC controls at this time

Wait 40 seconds for the HVAC control module and actuators to re-calibrate.

I've always had the best luck at this point by turning key off. Removing
key and closing the door. (Signals the BCM of a completed driving
cycle)

Then climb in in, start and drive.

If that doesn't fix it, I'd have the codes read, if any for the auto control unit