Jrogville
Member
What comments about the Rear HVAC Assembly did the service people make to @ussmd?
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I referred to this. I would expect Tesla service techs to know about such things as refrigeration lines, but who knows:
So, to me it seems the rear HVAC assembly being a blower with temperature actuators seems a solid baseline guess. Whether it might have any other features, I don't know.
Jrogville
Member
I see. Air conditioning systems consists of two basic components. The compressor, which expels heat and the evaporator that absorbs heat. That's how you pump heat from inside the car to the outside. You can have just one compressor that expels heat from multiple evaporators. In this case (perhaps) one evaporator at the front for the dash vents, and one at the rear for the rear seat vents. Passing air over evaporator coils is what sucks the hear out of the air and cools it before it is sent into the cabin.
The more that I think about it, it wouldn't make any sense to have just a fan at the back of the car. All it would do would be to pump warm air to the rear seat vents. The air needs to be cooled. And you would have huge transmission losses if you cooled the air at the front of the car and then sent it all the way to the rear of the car before blowing it out the rear vents.
Having an evaporator at that rear location would cool the air closer to those rear seat vents. By in essence splitting the car into two cooling zones, you can design a lower capacity A/C system because the air doesn't have to travel as far (lower transmission losses). Over distance, the air will warm up and not provide as much comfort to the passengers. That's why the cooling is less effective for the 5-seater, because all the air (either directly from the dash vents, or thru ducts) has to come from that one evaporator at the front of the car.
Back to the basic discussion, it really is a false economy to deprecate the A/C system for the 5-seat cars. You still have the same volume and just two seats less. Maybe they figured with 5 seats it's like the Model S and that only has one system. But that's wrong-headed because the Model X has a much larger volume (and the rear seat cooling in the Model S isn't that great in my own experience).
In terms of upgradability, I don't think there's much chance for existing cars. You only have half the number of rear vents in the 5-seater, and with the same fan configuration, the air velocity would be much higher and therefore noisier. And the ducts are coming from the wrong direction anyway.
I don't mind being "fact checked", and you are correct about the V8 as I also just checked. However, there was something about the 2008 or 2010 GX that caused them to reduce the size of the A/C compressor, at least that's what the dealership service guy told me, along with the factory spec of "40 degree from ambient". In my aging process, I must have "confabulated" it was the drop in cylinders, but so far all online research say 4.7L V-8.
Anyway, that experience is why I am A/C neurotic, plus living in areas with summers with months over 100 degs since 1980.
This is now the 2nd SUV I have owned with A/C cooling issues, but with the Tesla it's airflow.
I too am perplexed about this rear HVAC assembly mystery...I think the diagram by @AnxietyRanger in post #52 confirms it as the additional unit only available in 6/7 seat configs. That missing hardware may also allow for the extra width of the rear cargo area in the 5-seat config, but that is pure speculation given the location.
@Jrogville also make a good point about the distance between the A/C Compressor up front and the suspected 6/7-seater rear fan in the back, as this would truly need an insulated refrigerant line to connect them.
Also consider the change in the ducting Tesla did with the 5-seater design,changing the B-pillar vents air source from the rear unit to the front unit. Again, the reduction of max airflow between the different configs is very obvious to anyone checking it out. Did they just not care about the almost 50% reduction in airflow? Again, an objective windmeter is not required. Perhaps that is what irks me the most.
While each of us in time will be able to evaluate the impact of lack of a rear fan system for our passengers in the summer heat, I predict it will be a manageable deficit, definitely with pre-cooling, an optional investment in thermal tint, and knowledge about closing down some front vents if necessary.
However, maybe Dyson can come up with some 12v bladeless fan with a Tesla logo... or one of these USB-powered perhaps
@Jrogville I understand what you are saying and also how split A/C works as I have bought such systems to home.
However, I also did a fair bit of reading on automotive rear HVAC modules and most of them were blowers with temperature actuators. Some has extra heaters and rare examples had refrigeration lines for dual A/C.
Your theory is valid, I just don't see the supporting evidence on Model X for it. Is it possible I missed something? Sure. I don't know what the full feature set of that rear HVAC assembly is.
However, I also did a fair bit of reading on automotive rear HVAC modules and most of them were blowers with temperature actuators. Some has extra heaters and rare examples had refrigeration lines for dual A/C.
Your theory is valid, I just don't see the supporting evidence on Model X for it. Is it possible I missed something? Sure. I don't know what the full feature set of that rear HVAC assembly is.
Do you mean this extra slice of space on the late VIN Model Xs?
I think that is only unrelated space optimization as my six-seater has that space as well. Unless five seater has even more?
Incidentally right side did get less extra space as left side in this optimization, which would suggest a bulkier component behind right side (the wide rear HVAC) as opposed to left side (flat charger box).
Trying out wrong VIN Tesla mats and third-party Model S goodies on Model X
jgrgnt
Member
Maybe it is for both?
My car (pictures are from my car) has UHFS and is 6-seater so has rear HVAC assembly there as well.
Good posts both @essmd and @Jrogville. Interesting to see where this detective work leads.
Still, the blower action seems to be the most obvious concern with the five-seater. That much is clear. @essmd provided nice measurements!
Still, the blower action seems to be the most obvious concern with the five-seater. That much is clear. @essmd provided nice measurements!
Jrogville
Member
I don't disagree with you at all. All that I was saying is rank speculation. You certainly have done more research than me. My only foundation in fact for speculating beyond the Rear HVAC Assembly being more than just a fan, was the high voltage wiring to feed it. I didn't see why a fan would need 240V, while an evaporator does to work efficiently. Then back to speculation, it didn't make sense to me to move the cold air all the way to the back of the car to then move it to the rear seat vents, although that's entirely possible.
@Jrogville Indeed, I don't know if an automotive blower would need high-power either. Maybe? Maybe not?
Ahh, I understand now there is a universal increase in width, since I only compared the rear width difference between my 6-seater and a new 5-seater. Thanks for the education.
As far as what that rear HVAC element is from an anatomy or functionality perspective, it may be a moot point, since the current result is clearly reduced, possibly inadequate, airflow from the B-pillar vents when the singe fan is on MAX (11).
Every 5-seat owner who test drove a Model X last summer and felt adequate 2nd row A/C airflow has a legitimate complaint about this deficit. Short of retrofitting each 5-seater with a rear booster fan or increasing the existing fan's output , I am not sure what can be done at this point... other than add some cheezy 3rd party fan as previously mentioned.
I could see Tesla making some changes to future production, but I agree it seems quite problematic that this level of quality has seeped into production. Maybe some retrofit fixes could be offered to existing fleet as well?
Jrogville
Member
Unfortunately, I don't remember many instances of Tesla going back and correcting poor decisions on already produced cars. Like you said, better chance they will correct it in the future, but there have to be plenty of complaints to motivate them.
They do sell a lot to hot climates. Might crop up?
Is it really so that this wouldn't be a worry in California, if it is a worry in Florida, as some suggest?
I have made several comments in the past that Tesla seems to be very "Californian" in their decisions, at least in my opinion (ie- choice of fashion over function in 6/7 non-folding seats, lack of onscreen SMS integration for phones like in other vehicles) and this one may have to do with the overall moderate climate there.
Silly prediction, but if Tesla was based in Phoenix, I guarantee that the A/C functionality would be a priority.
Jrogville
Member
This will definitely kick up in intensity as we get into the summer months. Remember the car has only been used in winter and spring weather so far. Of course, the southern hemisphere would be the opposite, but beyond Australia there may not be many markets there. Is China southern hemisphere?
I think the problem is that Calif is a lot dryer than Florida in particular, and probably a lot of mid and NE states as well. The lower humidity means that you will be comfortable with a somewhat higher temperature. Only to a degree, of course.
A genuine question, I understand there is a difference in the heat/humidity in different parts of the world, but is California really not hot enough to suffer from a potential issue with rear AC?
Thanks for the explanation.
And yes, I agree with @essmd that Tesla is quite Californian in many features...
I see you are EU, so may not be familiar with the dramatic summer climate variances in the U.S.
Hating to sweat and having lived in NY, Mn, Fl, Ia, Ne, Az, Ca, and now Tx, I have a clear understanding of the essential need for good A/C in the home and car.
The key factors that impact the functionality for adequate A/C is heat and humidity.
Overall, California is not very humid, despite being on the coast, since the Pacific is a cooler ocean compared to the Atlantic, and the climate is impacted by the prevailing W to E winds, the ocean, and the mountains.
Southern Ca on the coast is almost always a beautiful temperature (San Diego, many don't have A/C in homes, up through the Bay area), and the further north the cooler the summers are (San Francisco is delightful in the summer, mostly unless a heat wave) . Once you get inland however, the air dries and temperatures can soar as approaching Arizona and Utah. Death Valley, Ca is the hottest and driest location at times, then the other western states.
Florida is completely different, for the southern peninsula has very hot and humid summers where the A/C is more challenged for cooling.
The rest of the U.S. also has significant summer heat variations, as the upper midwest (ie - Omaha, Neb) can be just as hot and humid as southern Florida.
The southeast U.S. is reliably hot and humid in the summer, as can be parts of the Northeast
A Model X with all the overhead glass in the summer can reach temps of over 140 deg F or 60 deg C, so forgetting to pre-cool can be a miserable environment to get into, and the ability to cool off the cabin off quickly depends on cooling capacity of the compressor and airflow.
Plus for humans to cool, the better airflow of cool air, the more comfortable as evaporating sweat helps to cool..
Science lecture over...more than you probably cared to know, but some insight to how Tesla may have missed a significant detail when removing the 2nd fan.
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