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Discussion Starter · #1 ·
I'm attempting to convert my 04 tiburon from manual HVAC controls to automatic & things have been going smoothly other than one problem. The manual thermistor has 3 wires and cuts power the the triple switch completely, where the auto HVAC uses a two wire thermistor that is used as a sensor only. As a result, I'm presented with three options:

1) Remove the original thermistor & bridge pins 3-2 to bypass it in the harness & replace it with the auto HVAC thermistor & wire that directly to the module.
-This would be the "ideal" option as far as proper wiring goes, but it means I need to get to the thermistor, and that might require disassembling the HVAC assembly to do.

2) Rewire the original thermistor to be used by the auto HVAC controller.
-This would be my ideal solution, however, I have no idea how the two differ from each other. they're clearly different per the diagram, but I don't know how they work or if I can adapt it to work with the auto HVAC.

3) Leave the original thermistor as it is & install an auto HVAC thermistor as a dummy switch to make the auto HVAC module happy enough to turn on the A/C.
-The default value for an open evaporator sensor is -2C, so it likely won't turn on the A/C as a result of the default value being below freezing. This would be the easiest option to wire as all that would be needed to be done is to put a dummy sensor (I.E. a resistor) in the harness, but I'm not sure how the auto HVAC uses the thermistor or if it'll cause issues.

The temp, mode, and recerc actuators work fine with the auto HVAC, everything else is as simple as connecting pin A to pin B and so on but this thermistor problem is outside my comfort area so I'd like some input if anyone has any idea how these things work.

For reference, this is the manual climate control thermistor setup:
Schematic Font Slope Parallel Rectangle


And this is the Auto thermistor setup:
Product Azure Font Schematic Rectangle
Slope Rectangle Font Schematic Parallel
 

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2) Rewire the original thermistor to be used by the auto HVAC controller.
-This would be my ideal solution, however, I have no idea how the two differ from each other. they're clearly different per the diagram
I know nothing about the system, but I have little faith that this will work. The sensor for the manual unit appears to be an ON-OFF thing, while the auto system clearly needs a linear feedback mechanism.

Where is that sensor located? Attacked to the evaporator core buried deep inside the air box?
 

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Discussion Starter · #4 ·
I didn't try to get to my sensor yet, I'm still routing wires for the various sensors I need to add, but the tiburon I was yoinking sensors from in the junkyard seems to have it buried in the HVAC assembly. What's pictured is actually the connector for the sensor, not the sensor itself. I was going to try to get the thermistor too, but it was 20F and snowing so I decided to let that one slide instead of trying to pull that whole HVAC assembly apart.
 

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Discussion Starter · #5 · (Edited)
Update: I got the blower motor transistor & high speed relay working now, so all I have left to do until my humidity and ambient air temp (these sensors were already yoinked from the doner car) sensors arrives is to mess with this thermistor. It looks like the thermistor is almost removable, but it doesn't look like it'll actually get out without splitting the case. However, I noticed something. The automatic HVAC doner car had just a simple connector next to the thermistor, but my car has a big black box in the connector's place. Three wires go into the black box, but only two wires go out of the box to the thermistor, leading me to hope the black box is doing the magic. I've ordered an auto HVAC thermistor & will poke holes in the manual's wires after the black box & compare values once it arrives. If I'm lucky, the readings will be the same on both. fingers crossed.
 

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Discussion Starter · #6 ·
Update pt 2: Turns out the auto HVAC still turns on the A/C request pin even with the evap sensor open code set when pulling codes out of the unit (hold auto + spam outside temp for codes). It has a separate output for the triple switch & turns that off with the evap sensor but not the A/C request, which the manual controls just has one output & that's jumped to both the triple switch and the ECU.

As a result, leaving the evap sensor circuit open doesn't seem to affect the operation of the A/C if you just use the A/C request pin & ignore the triple switch all together. There's a chance the unit uses the evap sensor to determine the temperature of the air going through the system, but I'd be surprised if it actually does that. It's probably just used as a "too cold" switch like the manual controls, which is still handled just fine by the manual style thermistor switch.

Swapping the manual controls for auto controls is actually not too difficult at all, provided you get all the necessary connectors / sensors from a doner car. The transistor / hi-speed fan relay were the most difficult part of the swap, but it actually worked out really nicely. I was able to get all the power / grounds cut of out the doner harness & spliced into my existing harness pretty easily and was able to send the three extra circuits (transistor control, hi speed relay, and blower motor feedback) through the old resistor wires to get them back to the control unit. Now all that needs to be done is to run the new cables for the ambient temp sensor & humidity sensor, which would be already installed if the doner car had them.

You really just need a junk yard that has a tib with the auto controls and to be vaguely literate with wiring diagrams.
 

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It looks like the thermistor is almost removable, but it doesn't look like it'll actually get out without splitting the case. However, I noticed something. The automatic HVAC doner car had just a simple connector next to the thermistor, but my car has a big black box in the connector's place. Three wires go into the black box, but only two wires go out of the box to the thermistor, leading me to hope the black box is doing the magic

There's a chance the unit uses the evap sensor to determine the temperature of the air going through the system, but I'd be surprised if it actually does that. It's probably just used as a "too cold" switch like the manual controls, which is still handled just fine by the manual style thermistor switch.
That's interesting. You're saying that even though it's drawn on the diagram as a three wire box, in reality it's a five wire box with three going to the controller and two others going to an external thermistor mounted inside the evap airbox?

If that's the case, then I agree... They might have used the same (or similar enough) thermal switch inside the airbox and you could just remove the three wire module and hard wire the sensor to the new controller. I wonder what is inside that module... The wiring diagram indicates that the only thing inside that module is a PNP transistor. Certainly worth a couple measurements with a meter.

I also agree that device looks like a "too cold" switch like they're using that to make sure the evaporator doesn't freeze up on high humidity days. In fact, if you look at that same device in the Elantra section of the manual (instead of the Tib section), they refer to it as the "evaporator temperature switch". Implication is that it's an on-off kind of thing.

So if that's the case, then where is the analog feedback sensor for control of the interior cabin temperature? Is it just built into the controller and they don't call it out on any of the diagrams?
 

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Discussion Starter · #8 ·
So if that's the case, then where is the analog feedback sensor for control of the interior cabin temperature? Is it just built into the controller and they don't call it out on any of the diagrams?
Yes, it's "internal" to the module. it's extra weird because if you look at the bottom left of SD971-2 you'll see an "in-car sensor" output & input, but they're just looped back to each other. This loop is in fact necessary, if it's not there the control module throws a code 11, but it's happy if you bridge those contacts. It's actually just bridged in the harness, I checked the doner car before cutting the harness & found 0 ohms between the pins.

The sensor is mounted to the back of the module & pulls air through the little grill on the bottom right, It's easily removable & replaceable. Good thing too because the unit I bought had a fan motor that wouldn't spin unless you gave it a push & made a pretty bad noise when it did start spinning. the doner car's sensor's motor was working fine & quietly so I swapped that into my unit. That fan behind the sensor is kinda important because it needs to pull air pas the sensor to get an accurate reading.

I'm probably going to leave it using the A/C select signal & leave the sensor alone unless I notice some odd behavior.

I'm going to try to get a measurement of the wires after the black box, but I'm going error on the side of caution. I can't find the manual style evaporator sensor anywhere so I'll be screwed into disassembling the HVAC if I accidentally break it. I'm going to wait until I get my auto-style evaporator sensor arrives so I can compare their readings.
 

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Thanks for filling in the blank about where the feedback sensor is. I've never seen any of it. The only time I've ever had anything to do with the HVAC system was to pull the control assy (manual style) out of the console to replace those light bulbs. So I'm trying to help with your quest, but admittedly flying pretty much blind. My A/C compressor seized up not long ago and I'm going to be putting in a replacement, but all of that work should be out in the engine compartment.

I saw that "in-car sensor" and it was curious to me as well. Clearly a signal to the controller module that it's installed correctly in a car. Maybe as signal to the controller so it can tell the difference between being installed in a vehicle vs. being on a test rig. Maybe the controller enters some sort of bench test mode if those connections are not shorted together or something. Speculation, of course.

So the switch on the evaporator core... Looking at the wiring diagrams, it looks like when everything is working correctly, that switch is closed, right? At least on the manual version.

And you're saying that the auto version still seems to work even with that switch disconnected completely? But it throws an error code? What are you using to get the error codes? Does it show on the display on the module, or are you going in through the OBD port or something?
 

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Oh, and out of curiosity... Any idea why they need both an ambient temp sensor and that AQS (Ambient Quality Sensor) thing? What does the AQS do? It's not humidity because they've got a separate sensor for that.
 

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Discussion Starter · #11 · (Edited)
So the switch on the evaporator core... Looking at the wiring diagrams, it looks like when everything is working correctly, that switch is closed, right? At least on the manual version.
Yes, The switch should be closed until the temperature drops below 1.5C, then it'll be open until it goes above 3C.
And you're saying that the auto version still seems to work even with that switch disconnected completely? But it throws an error code? What are you using to get the error codes? Does it show on the display on the module, or are you going in through the OBD port or something?
Yes, it works with it disconnected by shier coincidence. The manual controls have one output that gets sent to the ECU for A/C request, but it also goes though the thermostatic switch on a separate wire jumped from the same output to power the triple sensor. The auto controls has two outputs, one for A/C request & one for the triple sensor and it seems to only cut the triple sensor output just like the manual style would.

The codes are pulled by holding "auto" and pressing "outside temp" 4 times within 2 seconds. Codes are then displayed on the module's display & can be looked up by a chart in the beginning of the HVAC section of the shop manual.
Oh, and out of curiosity... Any idea why they need both an ambient temp sensor and that AQS (Ambient Quality Sensor) thing? What does the AQS do? It's not humidity because they've got a separate sensor for that.
The air quality sensor is mounted next to the ambient sensor & is suppose to detect harmful gasses & allergen. It'll send a signal to the control unit to cycle into recerc mode when it detects those conditions.

I was going to leave it out on my conversion because the AQS sensor I got from the doner car is actually bad, it's physically expanded the plastic case from corrosion. I'm still going to run the harness just in case I find one for a good price, but they're a little too pricey imo.

I always wanted a tib with auto climate controls but it was never in the cards whenever I was shopping for one, and my DD subaru has it & really drove home how awesome it is. So, I've been mocking this up on and off for a few years now & finally decided to pull the trigger when I found an auto control module for $20 & had a tib with auto HVAC move into a local junkyard.
 

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Discussion Starter · #13 · (Edited)
Gotcha. And I will at least RTFM between now and the next time so I can at least stop asking the questions who's answers could be found there. :)
No worries, I wouldn't expect you to read about the auto climate controls if you weren't interested in adding them.

I just found something out that is really interesting, Hyundai used the same engine-side of the harness for both the manual and auto climate control tiburons, at least for the 04 (even though USDM didn't even get the option for auto hvac). This means that you can skip making / routing the engine-side harness all together if you got the core-support harness with the AQS and ambient sensor like I did. The other side of the harness goes into the driver kick panel, making getting to the AQS and ambient snesor wires for the control module super easy.
 

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Hyundai used the same engine-side of the harness for both the manual and auto climate control tiburons,
Wow. So you've already got an unused connector for the AQS hanging empty out by the grill? That sure does make it easier to wire that in.

And I started to breeze through the HVAC section of the FSM and found one confusing issue so far... That In-Car Sensor thing. The manual talks about it as though it's the main feedback element for system control, but on the wiring diagram (as you mentioned earlier) it's shown as a short in the harness.

And since you measured a dead short in the donor car, I think there's a documentation error there. I think they used the same term (or wrong term) for two different entities. I think the documentation expects the In-Car sensor to be the interior temp sensor (with the little blower fan assy), but then they used the same term for that diagnostic loop in the harness. There is even a chart of resistance vs temperature for that "sensor".

You got an error code 11 with that loop open, but the manual seems to think you should get an error 12 if it's shorted. Doesn't matter much, just confusing.
 

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Discussion Starter · #15 ·
Wow. So you've already got an unused connector for the AQS hanging empty out by the grill? That sure does make it easier to wire that in.
Not quite, It's run all the way up to to the big connector at the bottom of the core support, but gets left out of the core support harness. You'll see 8 wires go into EE02 but only 3 leave (horn).
Automotive tire Automotive lighting Light Motor vehicle Black


While this doesn't give you the connectors you need, you can get a core support harness from a doner car like I did & simply swap it out. The only thing that harness goes to is the AQS, ambient temp sensor, and horns, so it doesn't go far & is easy to swap. Even if you can't get that harness, all the wires you need are right there for the picking, including power / ground for the AQS.

The In-Car side terminates to this harness:
Wheel Tire Automotive tire Automotive lighting Motor vehicle

You can just cut the wires and solder / crimp straight to them since the in-car harness isn't pinned for them, then run them to your auto HVAC harness. Despite how it looks, the highlighted harness is still the engine-side harness. it looks like it would be coming in through the hole in the kick panel, but the harness actually comes in through the grommet in the fender & runs on the inside to that kick panel hole.

You got an error code 11 with that loop open, but the manual seems to think you should get an error 12 if it's shorted. Doesn't matter much, just confusing.
My guess is it's in series with the in-car sensor & the signal physically goes through that loop. Maybe they bridge the contacts for the integrated in-car sensor & use those connector pins for a remote mounted in-car sensor for bigger vehicles? I donno, it's a bit confusing.

I just took it for it's first drive today & it preformed as expected. I doubt I'll be able to test the A/C side of things for half a year now that it's 20F, but I have confidence it'll work. The only reference I found for the thermistor is it'll cut off the A/C below 3C and it'll delay the blower motor for 9 seconds on startup if the evap core is above 30C. I can live with the manual sensor work around if the only side effect is that it blows hot air for a few seconds when I start the car in the summer.

I still say the hardest part is sorting out the blower motor controls, that engine-side harness was a serious bonus, lol.
 

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I often find subtle differences between the service manuals for the different models, and the HVAC section is no exception.

For example, looking at the Elantra HVAC section... Page HA-38 and 39 has some info about the evap sensor. And page HA-46 and 78 clearly label the sensor in the assy (with the little fan) as the in-car sensor.

So I don't know what value I'm really adding, but I'm glad to hear that your system seems to be working the way you want it, at least in heating mode. Hope the same holds true come cooling season.
 

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Discussion Starter · #17 ·
I often find subtle differences between the service manuals for the different models, and the HVAC section is no exception.

For example, looking at the Elantra HVAC section... Page HA-38 and 39 has some info about the evap sensor. And page HA-46 and 78 clearly label the sensor in the assy (with the little fan) as the in-car sensor.

So I don't know what value I'm really adding, but I'm glad to hear that your system seems to be working the way you want it, at least in heating mode. Hope the same holds true come cooling season.
I've learned to take the manuals with a grain of salt, for example, the in-car sensor has a response graph, but neither axis is labeled. 40C? 40 ohms? who knows! they don't tell you.

I got my auto evap sensor yesterday & left it in the car in my garage over night. It was about 60F in the garage, I found that the new sensor measured at about 14.5K ohms while the installed sensor measured at about 11.5K ohms. The new sensor dropped to about 9.5K ohms after holding it in my hand for a minute.

I'm not sure what to make of this info, but I thought I would put it out there since I had it anyway. It's not close enough where I would feel confident that they're the same w/o a chart to reference, and either the manual doesn't have one or I'm too dumb to find it.
 
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