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Old 11-11-2019, 10:16 AM
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Another AC blower motor issue... sigh...

Well, it's time to whip out good ole' 8W-42-3 from the TJ service manual. If you've ever had AC blower issues, you have looked at this page for over an hour probably.



On my 2001 TJ, I've run the gambit on this issue. Let's see... I've replaced vacuum lines when actuator doors don't open. I've replaced melted wiring harnesses, and ultimately the blower motor itself when old age made high current want to send my Jeep up in smoke. I've even replaced the good ole resistor pack when I couldn't figure out why position 3 on the blower speed switch never works (gave up trying to figure that one out when the resistor pack didn't cure the issue).



But this one is a new one on me. Everything works except for positions 4&5 on mode selector (vent panel and floor/defrost mix). Let's run through the typical troubleshooting steps:


1. Check vacuum lines. Pulled the one below the throttle body- check valve ok. The 'infamous T-connection' beside the computer was good too. Crawled under right side to inspect #8 below the battery... good. Hmm. ok next step.


2. Electrical. Pulled AC control unit. Nothing melted. Thank God, probably means blower is good (makes sense- it works in other modes).



I'm leaning toward replacing the vacuum selector switch, mostly because I've REPLACED EVERY #$#^@! THING ELSE. The lights have been burned out for years on the AC panel. Maybe this time I'll just get the whole dang unit and replace it.



Gonna see if I can verify that it's the switch tonight. Will report back with findings.

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Old 11-11-2019, 01:27 PM   #2
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If you are getting good blower function (all speeds) but having trouble with the mode selector settings the trouble is not in the electrical circuit.

The mode selector is all vacuum controlled.

Go to the Heating & A/C chapter of the FSM & find the vacuum controls section which has the vacuum diagrams for the various mode settings. From that you should be able to look under the dash & watch the actuators move as you turn the switch (have the engine running to get vacuum) to see which actuators are or are not moving when they should. You may have a non functioning actuator or one of the arms may be disconnected from its door or even a vacuum leak in one of the colored lines.

If any of the doors are not moving when they should you can remove the vacuum line for that actuator to see if there is vacuum to the line. If not the switch could be bad.

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Old 11-12-2019, 06:20 AM
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I disagree (respectfully, of course!).. follow my logic on this.


According to the electrical diagram, when the mode switch is engaged in positions 1-6, current exits at C3-B, re-enters at C1-E, where it moves through the blower speed switch. Current exits at C1-(A-D) and moves through the resistor block then to the blower motor or directly through the blower motor depending on if you're at max or not. Power is then drawn from the PDC assuming the blower motor relay has been energized by fuse 8 stemming from the ignition switch.


Nowhere in that path is a pressure sensor that disconnects power from the blower motor in the event of a vacuum loss, or an interlock that disconnects the circuit if actuator doors do not move. If there was a vacuum loss at any position on the mode-selector, the blower would be moving air through the defrost vent (the default open position when there is no vacuum present.)



But since the blower motor completely turns off at positions 3 and 4 (vent and heat) mode, I conclude that there is a short in the contact(s) at those positions which sends current over to the fan speed switch.



Since the lights have all burned out in my AC control unit, I went ahead and ordered the full head unit from Amazon (PN 55037473AB, $85 if anyone's interested... note that's for 97-05 Wranglers with heat and AC. If your Jeep is heat only, you'll need PN 55037472AB.) I could have ordered just the mode selector vacuum/electrical switch unit (PN 5013833AA) for $37, but since my LED's were shot, I opted for the full head unit.


does that make sense? Sorry I've only had one cup of coffee so far this morning
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Old 11-12-2019, 12:27 PM   #4
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Disagreement accepted. You are correct.

Were you saying in your first post the blower cuts out when the mode switch is in positions 4&5? Everything works except for positions 4&5 on mode selector…”

The way I read it you were not getting air flow from the proper vents when in those positions.

If the blower is cutting out only in those positions (4&5 or 3&4) then yes the mode switch (electrical contacts) is bad.

Just to clarify, while your logic is correct you misread the circuit. You followed the circuit properly but in the wrong direction. The current is moving through the circuit in the other direction. It is moving from relay to motor to resistor (except high speed) to speed switch to mode switch to ground. Everything past the motor is on the ground side of the circuit. Also, the mode switch contacts are not shorting, they are remaining open which blocks the path to ground.

All of the overheating you described over time it is not that uncommon & that can affect the mode switch too. Normally it will cause complete loss of blower function, not just some settings.

So with all that said, good work getting to the bad part.
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Old 11-12-2019, 07:11 PM
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Good catch- I'm an engineer but not an electrical one! Anyway, if this doesn't work, time to warm up the parts cannon!
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Old 11-12-2019, 08:05 PM   #6
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No! Not the cannon! Your troubleshooting has been too good so far. If you want to test the mode switch to be sure it is bad (or good) you can test for continuity between C3-b & C3-c as you turn the switch to each of the non off positions.

And no collateral damage (to your wallet)!
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Old 11-13-2019, 09:58 PM
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Well I replaced the AC unit tonight. aaaannndddd guess what. No power from the blower fan at any speed.

So since you don't know me, let me just tell you that I have the worst luck with buying parts. It took 3 radiators before I found one that didn't leak. Two water pumps. Two fuel pumps. No matter what part I buy, it never works on the first part. I always wind up spending an entire weekend replacing a bad part with another bad part, then I take it to the dealer, they put in another part, and it works. So tonight, I wasn't surprised that the AC module didn't work.

But I had an ohmeter, so I checked all the connections, switches, etc. Everything checked out. So, I got out the wiring diagram and decided to trace the entire circuit. I could have started with the battery and worked toward ground, but since I was replacing the AC unit (right next to ground), I started there.

Ground to AC: OK
AC control switch electrical connections: OK
Fan switch wire through resistor block, through the blower motor, and back to the blower relay: All OK.
I opted to check the blower motor by doing electrical continuity checks through the unit from within the cabin, everything ohmed out OK.
Next, I checked the blower relay and the AC clutch relay, fuses (at the PDC and in the fuse panel): All OK

So having verified that all electrical components were working properly, I engaged the ACC and started measuring voltages in the circuit. All parts of the circuit were energized, the relays were... relaying, the flux capacitor... fluxing. But no air.

So, knowing we had electrical connectivity through the motor, and voltage flowing... that could only mean one thing. bad blower motor? But that doesn't make sense... it was working on a couple of modes this afternoon when I came home! Why would it suddenly quit working when I was changing out the control head?

But, as I said earlier, my luck is the worst possible when working on cars. I removed the computer housing and wiggled the blower fan connector... voila... the blower came on. My blower fan makes this loud grinding noise when it's running, like you stuck a pencil in a fan. There was definitely some sort of connectivity issue at the connector- it was loosely connected enough to complete a circuit, but not tight enough to carry the high current load needed.

So I did what any PhD engineer would do- I squashed the connectors, flipped it around, shoved it in, cable tied it, put everything back together, put away my tools, and started to call it a night. But, maybe I should check one more time. It sounds like it's working... but let me get in the cabin and see how much air flow we have. ZERO. It was sucking in air actually.

Yep, you guessed it. I forgot my EE101 class about DC motors and what happens when you reverse polarity on the fan. It ran like a top though! Just in the wrong direction. So I had to take the computer back off and flip that cruddy connector back around.

So now I have heat- going to be in the lower 20's tomorrow morning. Let's hope that blower lasts the rest of the winter. If I have to replace it, do you guys have a brand you trust to work? Mine has the blonde colored fan housing- I saw a video where a guy replaced his with a motor that had a black housing. It ran a lot quieter, with a nice "woosh" sound rather than GGGGRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR. Thanks
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Old 11-13-2019, 10:40 PM   #8
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Well at least you got it fixed without resorting to the cannon. Thanks for posting results.

I have seen others with the fan connector causing that problem. Usually it causes intermittent loss of all speeds. I think the excessive heat like you have experienced causes the terminals to weaken & the fan’s vibration may also be a factor. If this persists you can always replace the connector or go to individual female spade terminals.

I have some info on replacement motors but will have to find it. Will be on the road tomorrow so maybe in a day or two.
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Old 11-14-2019, 09:30 AM   #9
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Your blower motor is bad. The windings are gone and thats what is making the resistance at the plug. If you you let it go the plug is going to melt
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Old 11-14-2019, 12:36 PM
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Quote:
Originally Posted by RUBI 4 MY MRS View Post
Well at least you got it fixed without resorting to the cannon. Thanks for posting results.

I have seen others with the fan connector causing that problem. Usually it causes intermittent loss of all speeds. I think the excessive heat like you have experienced causes the terminals to weaken & the fanís vibration may also be a factor. If this persists you can always replace the connector or go to individual female spade terminals.

I have some info on replacement motors but will have to find it. Will be on the road tomorrow so maybe in a day or two.

This is the one I purchased 2 years ago. Funny how the stock blower lasted 17 years, but the new one is struggling after two.


https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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Old 11-14-2019, 04:11 PM   #11
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I know, the OEM is usually far better than aftermarket & in some cases the later so called OEM from the dealer.


OK here is what I have. The first is a bit of a long thread but has a lot of info (as I recall, not going to read through it now). I do have a note that most of the “good stuff" is from about post 48 after about the first 5.

http://www.jeepforum.com/forum/f9/wh...y-die-3295145/

http://www.jeepforum.com/forum/f9/19...l#post34452297

http://www.jeepforum.com/forum/f9/bl...eeded-3955522/
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Old 11-14-2019, 08:13 PM
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OOoohhh... linking to another forum? Seems like VDO is the brand to avoid. I found a Motorcraft one on Amazon I think... at least it's a brand I recognize. The mopar was 3X more (of course)
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Old 11-14-2019, 08:27 PM   #13
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Notice that various "brands" look exactly alike. Same supplier?? I think there were references to some that were quieter & some that seemed to move more air too. The ones that cut out mostly on high speed are interesting. Probably a tighter thermo cutoff spec. Maybe not a bad idea but problematic if you really need high speed.





I remember when VDO was a very good brand.
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Old 11-15-2019, 07:03 AM
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I got the Autex... mostly because it didnt look like all the 500 other ones with the white basket (like I got before)... this forum has also got me buying LED lights too...I am more excited about that than having heat this winter.
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Old 11-15-2019, 12:48 PM   #15
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Good info on the Autex. Post good/bad results.
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Old 11-17-2019, 07:59 PM
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Well, the Autex had a white basket, which was unlike the amazon photo. Grrr. But, the stock connector went on nice and tight with the contact blades, and did not change speed when wiggled. So that's good. It made a satisfying "whoosh" sound, which is also good. So now with the new blower and new control head, I have constant heat, lights on the controls, and I won't be driving in fear of my center console going up in flames. I even got a chance to clean my battery terminals when I was installing the blower. All total it took 15 minutes to replace it (would have been 10 had I not dropped one of those 8mm screws.)

What I wish I had time to do:
1. Replace the stock green/black wire with a higher gauge wire
2. Double heat shrink blower wire and crimp on female couplers to hardwire to blower motor.
3. Install a relay so that the high current does not run through the control head. I could use the low current source from the blower motor relay to run through the control head and activate the high current through the resistor block and blower. The only bad thing would be I would need 4 relays (one for each blower speed setting), unless there is a 4-port relay on the market.
4. Disassemble the contraption where all the actuator doors are. There's probably a dozen screws and stuff that's accumulated in there over the last 20 years.

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