02 Yukon XL: No Defroster Air Flow, Blend or Mode Door???

[FlyboyTR]

During a trip this past week, we discovered a problem. After getting wet in the rain, temps had dropped, etc; we all got in, cranked up and I turned the unit to defrost. No Joy...just lots of fogged up front windows.

When pressing the A/C button, it would flash three times and then remain off. I believe this is normal from what I have read. I did confirm the A/C compressor was cycling on/off while in defrost mode, but there was no air flowing out of the windshield vents. Also, noted that when turned to Floor, there was virtually no airflow change. Everything seems to dump to the dash vents regardless of the flow setting.

Our system does NOT have the the split controls for the passenger/driver; just climate control for front and a rear system as well. So......

I have read almost everything on this site about the many issues revolving around this/these systems, but I am still not sure exactly where to start. The Recirc/Fresh switches brings on a definite sound change when activated (I assume that is good), The temp knob brings on an appropriate change to the outflow temp, but the directional flow control knob does virtually nothing.

I have tried the disconnect battery for a couple of minutes, reconnect, start motor and let run for 4 minutes, shut off, then restart after waiting at least 10 seconds, but no longer than 30 seconds. Still no change. There does seem to be a lot of variables in the re-calc procedures, but they are all similar.

So, which door controller do I need to repair/replace? In my case, is there a blend door for heat/cool and a mode controller to redirect the air to vent, floor, defrost? If so, which one is which? Thanks.

---------- Post added at 09:59 AM ---------- Previous post was at 09:48 AM ----------

Also, another piece of information. I have also read that battery problems can cause issues with the HVAC system. After sitting overnight, my battery voltage is around 11.8. When cranking the engine, my radar detector screams "low voltage." I have checked the battery several times and it always tests weak, but not bad (this is with a 100 amp load for 30 seconds). Charging is usually around 14.3 volts. Is it possible the low starting voltage/amperage could be causing an HVAC system calculation problem?

I may try to just hook up jumpers to our van (has a new battery), try the recalc procedure and see if it holds and the air flow portion works after that. Thoughts?

 

[Rivieraracing]

Sounds like your blend door actuator is done. Try jumping it with your van like you are talking about but if that doesn't solve your problem then I'd say you need to change out your blend door actuator.

 

[FlyboyTR]

Sounds like your blend door actuator is done. Try jumping it with your van like you are talking about but if that doesn't solve your problem then I'd say you need to change out your blend door actuator.

Chris,
Thanks for the reply. How do I determine which unit is which. Would this be the one by the accelerator pedal or under the hush cover by the floor vents on the passenger side?

Thanks!

 

[FlyboyTR]

OK... I found a short thread with this explanation. I hope it is accurate for my 02 Kon. If so, it sounds like I need to remove the servo located above the accelerator pedal. Once I remove the servo and unplug it, can I turn on the key and manually manipulate the mode door to ensure that all is working on that end? If I do that, where do I reset it prior to installing the new servo?

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scottg918514
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Join Date: Sep 2010
Name: Scott
Age: 44
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I believe the part is the same as blend and recirc.

Blend is under passenger kick panel, easy
Mode is behind center console, accessed from drivers footwell, also easy
Recirc is in between firewall and dash, hard the whole dash needs to come off.

 

[FlyboyTR]

I took the servo apart. The large gear inside the servo appears to be split from the teeth to the center hub. This appears to be stopping everything when the split reaches the gear on the little potentiometer/position sensor; since the gears no longer mesh at that point. I have ordered the new part, Dorman 604-113 from Amazon.com for $50. Should be here Tuesday.

I Took the advice that Sparky had given about leaving the large piece attached to the air box and forcefully separating the servo from it. It did take some pressure to hold the large movable plate/actuator and then pulling the servo off the shaft...but I did manage to get the servo to pull off, leaving everything else in tact.

I will update when the part comes in and installation is complete. Now, I'm off to work on that blasted mirror, again...

 

[Rivieraracing]

Sorry, for some reason I didn't see this thread again until now! Glad you found the broken one, was gonna tell you to change your temp on your heater and listen for which actuator moved which would mean the other one would be your problem one!

I've never had to mess with mine yet since I've owned the truck so I'm not much help for you on this! Good luck with the replacement!

 

[FlyboyTR]

Sorry, for some reason I didn't see this thread again until now! Glad you found the broken one, was gonna tell you to change your temp on your heater and listen for which actuator moved which would mean the other one would be your problem one!

I've never had to mess with mine yet since I've owned the truck so I'm not much help for you on this! Good luck with the replacement!

Great idea! I had not even thought about chasing the rabbit the way you described. I put that one in the keeper sack! Thanks!

 

[Rivieraracing]

Great idea! I had not even thought about chasing the rabbit the way you described. I put that one in the keeper sack! Thanks!

 

[chef choy]

OK... I found a short thread with this explanation. I hope it is accurate for my 02 Kon. If so, it sounds like I need to remove the servo located above the accelerator pedal. Once I remove the servo and unplug it, can I turn on the key and manually manipulate the mode door to ensure that all is working on that end? If I do that, where do I reset it prior to installing the new servo?

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scottg918514
Senior Member
Full Access Member

Join Date: Sep 2010
Name: Scott
Age: 44
Posts: 258
Default
I believe the part is the same as blend and recirc.

Blend is under passenger kick panel, easy
Mode is behind center console, accessed from drivers footwell, also easy
Recirc is in between firewall and dash, hard the whole dash needs to come off.

Hey bud, having the same issue, can you share that thread so I can check it out?

 

[FlyboyTR]

Hey bud, having the same issue, can you share that thread so I can check it out?

Brian,
That came from a very short, 2-post thread: http://www.tahoeyukonforum.com/forum/showthread.php?t=48816&highlight=blend .

I can't speak on what it takes to remove/replace the servo on the passenger side or the fresh air/recirc door...but I believe I have the "mode door" thing figured out; it is the one above the accelerator pedal. Please feel free to ask any specific questions and if I know the answer, I, and others, will be glad to help. My new servo came in yesterday and I will be installing it today. If possible, I may shoot a little video showing the unit.

One thing I had read on one of the many threads regarding this subject; was to NOT remove the the part that is attached to the servo. It is a large, sort of round disk that connects to several different things. This is the part the servo motor turns back and forth, depending on mode setting (vent, floor, defrost, etc). It is connected to several different gears/arms, etc that actually move the doors. Removing it, along with the servo, seems like the thing to do...until you realize how difficult it is to get the various parts back in sequence.

This, disk has a shaft that extends outward toward the drivers side. That is the shaft the servo connects with. That shaft is round with a flat portion on each side. The servo had the mating female part that matches the shaft configuration.

Once the servo screws and power cable have been removed, the disk wants to come off with the old servo. Do not remove the disk. It takes a lot of pressure, but using your fingers and thumbs, FORCE the servo off the disk shaft while holding the disk in place. It took me several tries, and I thought I was going to tear the thing up, but finally, they servo popped off the disk shaft. Once that is done, you can manually rotate the shaft/disk with your fingers (with the key on and blower on) and move it to the various mode positions. By doing that, you will know that all of the internal doors are working properly.

When you look at your new servo, the output driver (where the shaft on the black disk inserts into) will be basically centered. You can rotate the black disk to the approximate center of travel, taking note of where the flat sides of the shaft are positioned; then holding the servo in it mounting position/angle, the flat spots on the shaft should almost mate up to the servo. Gently place the servo onto the shaft and gently rotate it a few degrees back and forth until the flat notches line up with each other. You will be able to tell when they line up. The servo should be very close to it mounting position. Push the servo firmly onto the shaft, then rotate the servo body until the mounting screw holes line up (again...this should on be a few degrees (probably no more than 1/8 turn). Install the screws and power connector.

I have read that it is possible to get this thing 180 degrees out of sync. But, I believe it would take rotating the black disk past it's limits (and it will stop turning when it has reached it limits...while turning by hand); but I guess it is possible to force it past those stops.

Sorry to be rambling on... hope it helps. Again, feel free to ask any specific questions.