"Diagnosing" HVAC Issue

billlaaayyy

billlaaayyy

Member
Joined
Dec 28, 2021
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32
Location
Boston
Hi all,

first post after returning to the TJ club after a 15 year hiatus - picked up a 2005 TJ SE (with the 4L) and will have a list of to-do's for it. Right now as winter settles in, what is getting me most is diagnosing the HVAC issue that seems to hit plenty others where I am only getting defrost blowing.

I've traced all of the vacuum line and seems intact, in fact it looks like it was recently replaced before purchasing as it's near spotless. On the HVAC control panel, the fan levels all work (off, low, medium, high) as does the temperature. The location of the blowers does not other than OFF. I can turn it off, but any other option goes just to defrost. I've poked around under the dash and seems all the control arms are OKAY (one is easily accessible under the drivers side dash, one is not - and one is semi accessible behind the glovebox). The HVAC control panel is marked as '00 Wrangler so seems that was replaced already before - but am wondering if because it does go off to just on, is it the control module there or something else? Where do I try and troubleshoot next without ordering a bunch of parts and pulling the dash off? To add to my semi confusion, RockAuto lists 55037612AA as one option to order (which has the long vacuum lines that are needed), and I can find what seems to be an equivalent on Amazon which the listing shows is a replacement part, but only lists '99s-'04s. Free returns so might try.

Any suggestions for trying to better trace next possible root problems?

Thank you :) :)
 
No definite answer for you but this will bump you back up and maybe someone will chime in.
Sounds like you’re on the right track. I’ve read many other posts on here with your same problem and it’s normally vacuum related or the actuator arm is broke. The later is what I dealt with. It can be tricky because the arm of the actuator moves and appears to be doing its thing but it’s broken inside the box. I ended up taking the wire loop off the arm and moving with my fingers. It was obvious to me at that point the arm was moving to freely. I drove a wood screw into the end and yanked it out. Replaced and haven’t had an issue since.

There are lots of “How To’s” on here for doing a smoke test to check for leaks. The high percentage of time it’s from a vacuum fitting behind/below the battery box.
Good luck
 
Thanks - will check on that tomorrow! Did a smoke test (or tried?) and didnt get any spots worth noting as it related to the vacuum hose. Another post suggested a vacuum gun to better narrow down potential points of failure, so have that in the back of my mind as well. We shall see how it goes
 
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thought I was going to luck out and it be a bad switch and ordered a replacement panel. no luck. Based on another post (or was it youtube) someone suggested an easy way to verify the vacuum is good, is to undo the harness from behind the heater panel on the dash, cap the black line with your finger while running, then turn off the car. If your finger stays stuck (vacuumed) to the harness, the vacuum is good. Sweet, at least I was good to that point. The ac/heat blend door actuator i can verify works manually and per the controller, and all speeds of the blower work. It's just ONLY defrost no matter what. So either possible holes in my hvac harness (will look that over again) or one of the other door actuators. Will continue to troubleshoot....womp!
 
I just had this issue on our '03 (and I'll admit that I may have lucked out), but all I had to do was remove the vacuum line from the actuator and manually cycle the arm, then reconnect it.
I was almost prepared to gut the dash and pull out failed components, but I decided to try the easiest approach first.
I ended up not even having to remove the control panel.
It took me less than 10 minutes and zero parts.
 
WestCoastDan said:
I just had this issue on our '03 (and I'll admit that I may have lucked out), but all I had to do was remove the vacuum line from the actuator and manually cycle the arm, then reconnect it.
I was almost prepared to gut the dash and pull out failed components, but I decided to try the easiest approach first.
I ended up not even having to remove the control panel.
It took me less than 10 minutes and zero parts.
Click to expand...
wow that's one I have not read anywhere on the 100 posts, forums, youtube! Will give it a go, never know. If i reach under, I can push the actuators and that changes the heat - SO, my deduction (wrong or not) is that at least the internal arms are working and moving what needs to be moved. Just, the actuators are not - so perhaps something between the dash out to the actuators. Time to putter around some more
 
One other....wildcard, and duh I should have included this to start. It is a 2005 TJ. From reading part numbers on either RockAuto, or elsewhere, supposedly the hvac controller changed from 2004 to 2005. Honestly it looks all identical, and the part numbers from the FSM and part guide all match anyway - quadratech even said "if the parts numbers match go for it, its just an issue on our inventory system" - which 100% could be correct. Bought this one used a month ago, and when pulling the HVAC control it is marked as '00 Wrangler, so it was already swapped once prior to me. So either you truly do need an entirely different panel for the '05, or its another issue somewhere. if its the panel, then no amount of troubleshooting is going to get me there...
 
Mall'er said:
Here is something interesting I found. Maybe grab some calipers and see if you have the same issue?

https://www.jeepforum.com/threads/2006-tj-heater-control-module.4361453/
If you connect a mity-vac or something of that nature to the lines at the panel, can you apply vacuum to test the actuators?
Click to expand...
oh jeeeeezeeee! WELL, that would at least explain why so many listings do show the 05 being different and this could indeed be creating a leak AT the switch. Because they (previous owner) swapped in an older '00 hvac control that may be the underlying issue, Will see if i can test the actuators! Hmmmm another piece of the puzzle - THANK YOU for finding that!!!!!!
 
They (PO) may have had a hard time locating a panel that is '05 specific, or a hard time justifying the extra expense and just figured the difference wasn't significant..

Wouldn't it be a gas to find out this is why they sold it?
 
RIGHT???? We shall see. it could be a reason they gave up on it? Amazon had the 04 panel for $65 and the '05 panel is like $165 - free ship free returns. Could order that and test, and if that is it - know I still came out ahead of going to a shop. Or as I think about it, might try the heat-shrink tip to thicken up the connections and see if that helps at all. That would be nuts, but...also makes sense if its just not snug enough to keep the vacuum. Fine to the panel, then nada.
 
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are you actuator arm working ? the ones on the driver side just about at your right leg. my 97 was doing the same thing and 2 of the arms were broken
 
tr21triton said:
are you actuator arm working ? the ones on the driver side just about at your right leg. my 97 was doing the same thing and 2 of the arms were broken
Click to expand...
both arms seem OK! I can move them from the actuator with my hand, and the modes adjust. I disconnected the vacuum lines from the actuators, and while i change modes, I do *not* feel a vacuum coming through the harness. So, possibly a block in those lines, or crack, orrrr the switch and the diameter of the connections. I will give the heatshrink mod a test and see. Per the poster on JeepForum, that made his non-compatible unit compatible.
 
i dont know if yours is different, but mine has 3 arms. 1 for the defrost door, 1 for the dash vent door and 1 for floor. my defrost was broke in the open and the vent 1 was also broken but was closed.
 
Yes, the 2005 is different than the 97. Dont know which year changed, but driver side down underneath we have these 2 actuators instead of 3. The top actuator is easy to see/access and I can #3/#4 easily enough and get it onto the floor. The lower one, the image is actually deceptive as that is essentially looking UP at the actuator arm from under the jeep. that arm is under the panel stretching under the base of the dash so its harder to manually move.
1641425723125.png
 
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Mall'er said:
Here is something interesting I found. Maybe grab some calipers and see if you have the same issue?

https://www.jeepforum.com/threads/2006-tj-heater-control-module.4361453/
If you connect a mity-vac or something of that nature to the lines at the panel, can you apply vacuum to test the actuators?
Click to expand...
THIS. WAS. IT!!!!

Legit, wow! THANK YOU for digging this up and sharing it!! As I had determined, the vacuum was working to the dash, and it seemed that all actuators etc were still functioning (meaning I could move them manually) but there was no vacuum getting to them. What I can deduce (entirely speculation) is this.... the previous owner had some sort of HVAC issue, and replaced the control panel. Problem was, replaced it with a '00 version which is not (was not) compatible with the '05. That did not work, so also replaced the vacuum line, still didnt work (as we now know, because the '00 hvac panel is a different size port). So ultimately I have an '05 with a brand new vacuum line and an '00 hvac panel (caveat below) that was only blowing defrost. I followed this post and used 50 cents of heat shrink to thicken up the ports on the control. Now connecting the vacuum lines is much more snug, and ALL modes of heat blowing NOW WORK!!! So basically vacuum got all the way to the unit, but the size discrepancy at that connection created a vacuum leak, rendering the modes all broken. Adding the heat shrink (2 layers) was enough to fix it!!

My caveat is/was.....round 1 I used too much heat, and melted the small ports on the original '00 version that was in my jeep. I had ordered a replacement from amazon for $60 and then attempted on that muchhhh more carefully with the heat and was successful with the fix. So, would have been a 50 cent fix, but now had to keep the new panel Which is also OK because all parts and lights in it work better and brand new versus the older one. ANDDD still better than ordering the $180 version specific to the '05.

TL:DR. A little bit of heat shrink will make the '99-'04 hvac panel compatible with the '05 :)
 
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