HVAC mode door question

[alaskaman444]

I recently purchased a 2001 GMC 2500HD crew cab 4X4 w/Duramax engine. Here's my question: Should the two geared wheels above the HVAC mode actuator (on the drivers side above and to the right of the throttle pedal) stay engaged to each through out their entire movement? or are they supposed to disengage from each other during normal operation.

Here's the deal. When I put the mode switch on the dash to floor heat I'm not getting hardly any air movement. When I checked the HVAC mode actuator to see if it was working it seemed to be working fine; but I noticed that the two gears above it were disengaging from each other; and then would re-engage almost seamlessly. While this looks correct it might not be. Hoping someone on here might know for sure.

I live in Fairbanks Alaska so of course I need the heater to work at its best all the time! Any help with this would be greatly appreciated. Thanks in advance!
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[chevyburnout1]

That is the correct way for that actuator to work. When you say your not getting much air flow to the floor, are you getting correct air flow in the other modes (vent, defrost)? Does your fan sound like it's working very hard?

EDIT: It's an 01 so there is a possibility that your cabin air filter is clogged. Have you checked that? Should be a little trap door located on the passenger side of the HVAC case.

 

[alaskaman444]

Haven't had a chance to check that yet. Yes the air flow is correct through the other functions; just not much air flow. Sounds like this cab air filter will be a good place to start. Since I just bought the truck and have replaced all the other filters/fluids I'll just replace that one anyways. Thanks for confirming the proper operation of the actuator. I own factory service manuals and they didn't offer much for information concerning that. Needed to check with someone that knew for certain that what I was seeing was the correct operation before I started chasing my tail with that! Again....thanks! :thumb:

 

[alaskaman444]

It wasn't the filter. As a matter of the filter wasn't even there. I guess I'm taking the air box a part next days off. I'm hoping the cam for the heater door is just disconnected is all that's wrong. Most junk yards up here want to sell you the whole air box; not just the parts you need. This is gonna be a challenge I think! Better than paying someone else to do it though!

 

[alaskaman444]

Well...for the 235 of you who viewed this here's what I eventually found. Someone at some point had replaced the heater core (not me). When they were going back together with the air distribution ducts and IP mount they didn't quite get the ducting installed correctly. In fact there was a 1/2" gap between the air box and the duct assembly; so basically most of my heat was being dumped under the dash itself. The wiring harness that lays on top of the channel iron that comprises the "back bone" of the dash ended up being in the way of the door that controls air flow to the louvers; this all but broke the actuator lever. Got all that fixed and the wiring harness installed out of the way correctly. Ended up having to add some foam seals here and there because the duct assembly was warped from being out of position and heated who know how many times like that. So... now I have good air flow going to the floor again (well...at least as good as its gonna get. I don't like the design of the air flow through the air box)! Word to the inexperienced...be careful when disassembling and reassembling the dash. Make sure everything is where its supposed to be. I didn't see anything wrong until I removed enough of the dash to be able to get a good at the parts and pieces!