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A/C Effectiveness in 5-seat configuration - Predictions?

Discussion in 'Model X' started by essmd, Mar 8, 2017.

?

Will 5-seat A/C cooling be as effective in high heat (> 95 F) as the 6&7 seat config?

Poll closed Mar 22, 2017.
  1. Yes

    28.6%
  2. No

    42.9%
  3. Too early to tell

    28.6%
  1. AnxietyRanger

    AnxietyRanger Well-Known Member

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    Model S diagram does not show AC components so I do not think they are related to the drivetrain anyway.

    [​IMG]
     
  2. AnxietyRanger

    AnxietyRanger Well-Known Member

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    Compressor possibly being the same does not mean the rear HVAC would just be an extra controllable fan, though. With two more vents and software controls for the third zone there could be some extra hardware in the trunk...
     
  3. AnxietyRanger

    AnxietyRanger Well-Known Member

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    That rear HVAC component does seem fairly beefy. A second compressor? Heater?

    [​IMG]
    [​IMG]
     
  4. boaterva

    boaterva Supporting Member

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    We're all operating on little data, but, with one (say) compressor being strong enough to cool the battery (which is a lot of heat under supercharging), I would think it could be enough to cool the 6/7 without an additional 'back seat' compressor.

    But who knows, with what these diagrams are showing. We need someone to look inside a car. :D
     
    • Helpful x 1
  5. Jrogville

    Jrogville Member

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    The diagram in Post #34 identified the A/C compressor, the battery heater and the cabin heater, so the HVAC component at the rear of the car wouldn't be any of those. But the second drawing in this post make that rear component look like it includes a fan assembly of some sort.

    How's this for another wild supposition? That HVAC component in the back could be an evaporative coil together with a fan. Analogous to the inside unit of an A/C split system in a house. The compressor coolant is pumped from the compressor to this evaporative unit, which with the blower, sends the cool air to the rear seat vents. This location for the HVAC component would then make sense since this location is closer to the 2nd and 3rd row seat vents. There's no need for a second compressor in the rear. Remember that this diagram only shows high voltage lines, not coolant lines.

    One way to confirm this would be to see if there is condensation dripping unto the ground in this area when the rear AC is running on a humid day. I can see having a separate evaporator coil for the front dash vents because they would have a large load from the big windshield and preference to the front seat conditioning. This layout would be efficient because if there are no rear passengers, no fan OR cooling energy would be spent to cool the rear of the car, and the front evaporator would always have the same load whether there were rear passengers or not.

    What do you think?
     
    • Helpful x 1
  6. essmd

    essmd Phantom X

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    Not as dry as other places I have lived (Tucson, Fresno) but definitely drier than others (Houston, Phoenix, or the southeast).

    I have dealt with an inadequate A/C compressor, as when Lexus dropped the GX from a V8 to a V6, and downsized the compressor to save HP. At idle, it blew air only 40 deg cooler than ambient, the industry standard. So above 90 outside, it blew 50 inside, and that year we had over 60 days over 100, that's when I invested in stick thermometers.

    I promise most ICE SUV's blow cooler than a 40 degree difference, my LX and Cayenne never blew above 40 degrees despite the ambient temp, even on high blow.

    Yes, the A/C system not just cools, but also dehumidifies (hence the puddles of water in garage when Tesla is on), but can only do so well depending in the air circulation of the cabin, which is less in the 5-seater than 6/7 seaters.

    I (We) just have to accept that in the heat of the summer human 2nd row passengers may need the driver to close the front vents for max cooling effect, but my 4-legged kids will do just fine with the 2nd seats flat while I keep the A/C cranked.

    I hope that Tesla can reconfigure the fan speeds to compensate for this, but once again the Tesla Design team failed to think outside of their "California Box Mentality", and chose to remove the rear fan from a medium-sized SUV just because there was no 3rd row passengers... A BIG MISTAKE to many owners.

    I bet EVERYONE who prefers a 5-seater would have gladly paid the $200 cost of keeping in a rear fan control.

    Perhaps BMW, Mercedes, Lexus, etc may have done the same thing, but I sure wish Tesla would "out think" them on all aspects, and not just some of the features.

    Bottom line, Thermal-blocking tint EVERYWHERE (including windshield) may be critical in the 5-seaters located in the hot summer regions, the best being Spectra Photosync and Huper Optik, also the most expensive. After delivery last July, complete HO everywhere including above the safety line (legal but less thermal below) made a huge difference in sun radiation in the driver seat. That is first on my list upon delivery in June.
     

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    • Like x 1
  7. essmd

    essmd Phantom X

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    I really hope you get somewhere with this, but not holding my breath...
     
  8. essmd

    essmd Phantom X

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    Y'all can speculate all you want, but I know the facts cause for over a year I obsessed over the A/C system.

    I was supposed to get my '16 MX in April, but because I was concerned about the A/C effectiveness, I delayed my build until I had feedback from others in the Az heat that the A/C was adequate for an EV and a SUV cabin, plus some local testing of my own in June.

    There is only one compressor in all Model X's, confirmed by direct discussion with service techs. The only difference between the 5 and the 6/7 is the 2nd rear fan and the ducting.

    In the 6/7, the rear fan controls the B and C pillar vents, while the front fan controls the front vents and the vents under the armrests. In the 5, the rear fan is eliminated as is the C-pillar vents, and the single fan controls all of the circulation.

    In the 6/7 seater with the rear fan on 11 and all vents open, the b-pillars blow as much as 5 MPH on a wind meter, but in the 5-seater on a single fan the best the B-pillar blows is 3 MPH, unless you close 2 of the 4 front vents, then 4-5 MPH is possible.

    You don't need a windmeter to tell this, just your own hand, but I made it somewhat scientific.

    The only options for Tesla to improve the B-pillars airflow in a 5 seater is by increasing the fan speed to a higher RPM, or adding back a 2nd fan for just the B-pillar vents, the latter is very unlikely since only a limited number of owners will complain due to climate variation.

    Everything else is just a fairy tale....

    So complain away, just prepare to add thermal tint and close some of the front vents if needed.
     
    • Informative x 1
  9. essmd

    essmd Phantom X

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  10. AnxietyRanger

    AnxietyRanger Well-Known Member

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    #50 AnxietyRanger, Apr 28, 2017
    Last edited: Apr 28, 2017
    You did not anwer my or @Jrogville's point at all, though. Nobody is claiming there is a second compressor. But what is "rear HVAC assembly" where a "high-power cabling to rear HVAC assembly" runs to? This is in Tesla's own manual(s).

    You claim the only difference is rear fan and ducting (to the additional vents 3rd row). Fair enough, we know those differences exist, of course, in addition to software differences of two vs. three zones.

    However, neither of those in any way explain the "rear HVAC assembly" with a "high-power cabling to rear HVAC assembly" on the right side of the trunk. What is that and what does it do? @Jrogville is right in that it looks like it has a vent of some sort and the high-power cabling and presence in emergency guidance as a critical/dangerous components suggests it is more than just a simple fan. Would they need a high-power cable to run a fan? They would more obviously need it if it were, say, a combined additional heater with fan - just as a thought.

    [​IMG]

    [​IMG]
     
  11. AnxietyRanger

    AnxietyRanger Well-Known Member

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    #51 AnxietyRanger, Apr 28, 2017
    Last edited: Apr 28, 2017
    OK, the Model X Emergency Respond Guide does confirm the "rear HVAC" component is optional. Thus suggesting that is a part 6/7 seaters have and 5 seaters do not. So it IMO would not seem to be a drivetrain component as some suggested. It also confirms high voltage power is supplied to the rear HVAC (on the right side of the trunk) from the junction box integrated into the charger on the left side of the trunk - as shown in the images in messages above.

    If that is just a fan, it would seem to be quite a beefy fan!

    Here is a picture of the Model X rear HVAC assembly:

    model_x_rear_hvac_assembly.jpg
     
  12. AnxietyRanger

    AnxietyRanger Well-Known Member

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    #52 AnxietyRanger, Apr 28, 2017
    Last edited: Apr 28, 2017
    Been reading about this and apparently here are roughly four different types of HVAC modules:

    1) just a blower/fan
    2) blowers with temperature actuators, i.e. motors cutting cold/heated airflow as needed
    3) blowers with above, plus an extra heater
    4) blowers with refrigeration lines running to them basically creating front and rear A/C with just one compressor (e.g. Jgrogville's suggestion)

    Since there are no refrigeration lines shown in the emergency guide, and given @essmd's information, I find the 4) not likely. Number 2) seems very likely to me, I can't see how it could be just 1) and make a third zone. Number 3) we have no information on, just noting the possibility given the high-power line.

    Here is one car with refrigeration lines going to back, but just to clarify, there is no reason to believe this would apply to Model X:

    [​IMG]
     
  13. Jrogville

    Jrogville Member

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    How do you know there is no refrigerant line going to the rear HVAC assembly? The emergency guide only addresses high voltage components. A refrigerant line poses no danger by severing, so there's no reason to locate on the diagram. I don't know that there is one, I'm just saying we can't make the assumption that there isn't because one isn't shown on the high voltage components diagram.
     
  14. boaterva

    boaterva Supporting Member

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  15. vandacca

    vandacca ReActive Member

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    Great detective work @Jrogville & @AnxietyRanger. I'm on the edge of my 2016 Model-X vented seat. :)

    That was a painful series of photos to watch @boaterva. :eek: I hope that started as a totalled X.
     
    • Like x 1
  16. FURY

    FURY Member

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    I tried in vain to get the sales manager to allow me to order the "opttonal rear HVAC." but sadly that "option" did not present/nor was it allowed on a one off-no surprise on the latter. Maybe, just maybe, that will be a future option...

    Thank you very much

    FURY
     
  17. boaterva

    boaterva Supporting Member

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    Yeah, tell me about it... if not, at least it gave its life for a good cause!
     
  18. jgrgnt

    jgrgnt Supporting Member

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    It might require a combination of higher fan speeds and minor adjustments to the front registers to redirect more flow to the rear, and only when rear passengers are detected (or if the owner overrides through the UI, which would also need to be modified). Seems like the hardware necessary to accomplish this is already present.

    Off topic, but the US market GX never had anything less than 8 cylinders. They went from a 4.7 liter V8 in the first generation to a 4.6 liter V8 in the second gen. The only region with a V6 GX is China. We briefly looked at the GX since the wife has an older RX.
     
  19. AnxietyRanger

    AnxietyRanger Well-Known Member

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    True. I do not know. Just speculating.

    I just thought refridgerant lines might still be the kind of thing that is mentioned in emergency guidance (aren't they still kind of sensitive thingies?) and would be known to service people that have commented on the rear HVAC to @essmd...
     
  20. AnxietyRanger

    AnxietyRanger Well-Known Member

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    By optional I meant not fitted in every Model X. The emergency guide does not use the word optional, it merely notes "if equipped".

    Optional through selecting 6/7 seater.
     

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