AC switches from vent to defrost

[Hookmaster]

2004 Silverado. In the past 2 weeks with the AC on and coming out of the vents, it changed to coming out of the defrost by itself. Changing the selector did nothing. Both times it was "fixed" by turning off the engine and restarting. Any ideas on what to check? A few months after I had it, it wouldn't go to the defrost setting with the heat on. A controller board? was replaced that controls where the air goes to fix that.

[jwhjr]

I just had to switch out the blend door actuator a couple of weeks ago in my 04. My symptoms were that the driver side would start blowing hot and the only way to get it back to cold was to turn it off and then restart. Pretty soon that wouldn't work either. If I remember correctly, there are actually 3 of them in the truck and one of them may control what you're having an issue with. I did some searching online when my issue popped up and it looked like it is a common problem to have issues related to these actuators. Luckily it was the driver side one for me, the passenger side looks like a treat to replace. I had a small issue with the recalibration because I didn't have a scan tool to do it with, but I got it to work in the end. Good luck!

[Jeremy airjer W]

A scan tool will verify the problem as it will set a trouble code in the HVAC system (automatic HVAC).

To recalibrate you pull the HVAC/EBSC fuse in the underhood fuse block. Wait at least 10 seconds. Then turn the key to the run position. You should hear the various modes of operation switching back and forth. It will take roughly 40 seconds to complete, do not touch any of the controls during the recalibration.

[jwhjr]

Yep that's the recalibration steps I followed. I did it 3 times and it still wasn't working (I actually had the opposite issue, driver side was cold and passenger side was hot). The 4th time I did it, I pulled the HVAC fuse from under the hood and also the one in the cab and waited 15 minutes or so. When I started it back up the recalibration worked that time and it has been working perfectly ever since. Airjer - will any codes show in history even though I never saw any CE light? I have access to a scan tool up north and can check/clear those code(s) next time I'm up there if they're there.

[Jeremy airjer W]

The HVAC module will not turn on the check engine Light if there are any errors. You will need a higher end scan tool to look at those codes, data, or clear codes. Not sure how long there are retained before they are cleared after the problem is resolved.

[jwhjr]

I'll be up there in about a month and he has a higher end Snap-On scan tool, so if the codes are still there we'll see what they are and clear them out. Good to know that they won't show a noticeable code (CE light). Thanks airjer.

[Hookmaster]

It did it again today. Can the recalibration fix it without any new parts?

Airjer said, "To recalibrate you pull the HVAC/EBSC fuse in the underhood fuse block. Wait at least 10 seconds. Then turn the key to the run position." I assume you wait 10 seconds and put the fuse back in correct?

[jwhjr]

The recalibration may fix it if the only issue is that it is out of sync, and yes you put the fuse back in before starting. One question, did you have the battery disconnected at all before the issue occurred?

[Hookmaster]

It didn't start acting up until 2 weeks ago. Last fall I put in a new battery. The only thing that happened is the CD player spit out the CD that was "stuck" in there for over a year and now the CD player works great!!! I checked for codes last night and none were present, although it was working properly then. If it happens again, maybe I can try scanning it before shutting it off.