Model 3

HVAC question

Hi guys and gals. Does anyone know if the heater and ac in M3 draw a linear amount of power no matter what temp you’re requesting? I’m used to cranking the heater when it gets cooler out :) but if running it less than on HI will save I guess I’ll need to adjust.


  • edited November -1
    You are better off turning the seat heaters on and skipping the sauna routine while warming the entire cabin.
  • edited November -1
  • edited September 2019
    HI and LO should force the HVAC to the maximum, but really not necessary. If you set it to 70, and the cabin is very hot from sitting parked in the sun, the HVAC will run at maximum cooling to cool the cabin to 70. When it gets to the right temperature the fan and compressor spins down to maintain that temperature. it shouldn't get to 70 any faster by setting HI and then when the cabin gets to 70, you manually adjust it to 70. Heating is similar, but it does use a resistive heater.

    What is cool (pun intended) is the compressor runs at a variable rate depending on need. ICE cars use a clutch connected to the engine. So the compressor is on or off, and the speed is controlled by the motor speed, which is often unrelated to cooling needs. Seems like a Rube Goldberg system in comparison with Tesla's system.
  • edited September 2019
    That’s more the info I was wondering. Maybe I should have phrased the question differently (3am pop up idea Lol). From the little I understand about vehicular HVAC iCE motors seem to produce the same amount of heat no matter what and a dial controls the amount of heat that enters the cabin. Obvi that’s not great in an EV. Thanks for the input guys. Out of curiosity is there a better heating system than the “resistive”? Does Model X/S employ something better?
  • edited September 2019
    ICE produce waste heat, generally far more than is necessary to heat the cabin (although the North Dakota people may have a different opinion), so setting a “heat” temperature just changes how much of the waste heat gets dumped in the cabin, and how much gets dumped outside through the radiator. On a Tesla, heat is generated on demand from the battery; the more heat needed; the more range lost. A/C on the Tesla is similar - the battery drives the fan and compressor, the more cooling you need the more range lost. A/C has significantly less of an impact than heating, though.

    Are there more efficient heating methods? Yes. Heated seats are far more efficient because you’re heating a much smaller area, so need a lot less heat. A heat pump would be much more efficient - but would only work down to around freezing or so; you’d have to equip the car with resistive heaters anyway to deal with sub freezing conditions, which would raise costs. The Leaf, if I’m not mistaken, used a combination of heat pump and resistive heating.
  • edited September 2019
    A heat pump has the possibility of being more efficient in the proper application (usually a well insulated environment that does not lose heat quickly to the surroundings). A heat pump that has to run a 100% duty cycle, and take much longer to get a cabin up to temperature, may not be as efficient or work appropriately in many applications (I.E. frequent stops with opening and closing doors in cold temperatures). Heat pumps give the compressor a full time workout. Getting cabin temperature up quickly is a nice advantage to have. When you have a car that has over 200 miles range the minor energy "saver" to trade off for comfort is not much of a consideration for most.
  • edited September 2019
    @jrpierceii346 - I think others answered most of your questions. The S/X/3 all use the same cabin thermal system - variable-speed compressor for cooling and resistive heating.
  • edited September 2019
    When I parked in the office parking lot while the outside temperature is around 90, it gives bad smell whenever I start the car around 5pm. There are many people complaining about it. When I called the service center, they are asking me to bring the car to clean and replace the cabin filter. And they are asking $125. If everyone complaining about the bad smell, there is something wrong with the design and they have to fix it. We can not spend $125 every six months. Whenever we buy new car, we should enjoy it without issues for first couple of years. What is the other solution for this?
  • edited November -1
    @shekargn If you google A/C smells in cars you will find this is an issue that exists with some owners of cars from many different manufacturers. It is unclear if there is a design problem. Certainly if Tesla is charging some owners for the service they are not confirming something they would have to own up to in those cases. There is no data to understand how widespread the issue is and how many are affected. Some owners have reported in with no stink issues at all.
  • edited September 2019
    There are also many threads on how to clean your A/C system to eliminate the smell. Google "Klima Frank99" to see my posts on how to clean it, and "Lysol Magic 8 Ball" to see Magic 8 Ball's posts. There's no reason to continue living in fear of your A/C.
  • edited September 2019
    Tesla reportedly addresses the issue that @shekargn has in the following ways:
    a) As good will, no charge at all
    b) Labor is good willed, just the $35-ish price for new filters
    c) $125, as reported above. (If this includes the filters, suggests about $85 in labor.)
    d) just under $200, as reported by several (includes filters)
    e) $233 and no good will to do the decontamination (includes 2 filters that didn't need replacement - I got them back)

    I'm sure there are additional variants, but I am getting really peeved at Tesla's willy-nilly approach to the problem and what they are charging to (temporarily) fix it.
  • edited November -1
    @Frank, lots of us prefer not disassembling parts that need special tools to do. Cabin filter replacement in the M3 is absurdly complex relative to virtually any other vehicle I've had.
  • edited September 2019
    It takes one torx t15 (iirc) screwdriver. The only difficulty is that the screw is difficult to access.
  • edited November -1
    Frank99 | September 2, 2019
    It takes one torx t15 (iirc) screwdriver. The only difficulty is that the screw is difficult to access.
  • edited September 2019
    Hi M3s :-)
    I'm trying to set the HVAC to ventilation only, I mean, I want the system to just turn the fans and blow air from the outside, avoiding heating, cooling and ACing ... is that possible at all?

    What I see is that it is not possible to avoid the temperature set point, therefore the system will blow either heated or cooled air, never the plain natural air.

    Is there a trick to overcome the problem?

  • edited September 2019
    You can turn off the A/C portion in the environmental control screen. There is no way to prevent the heater from coming on....except by dropping your temperature down below ambient.
  • edited September 2019
    >You can turn off the A/C portion in the environmental control screen.

    Yes I did, but nevertheless:

    >There is no way to prevent the heater from coming on

    Exactly. That's what I want to avoid.
    In good old cars, there is a nice knob that does the heather/cooler switch off, you just tune the air intake by adjusting the fans, pretty useful when outside air is at the right temperature, that is, most of the time.

    With the M3, the option is to turn off completely the climate control and open the windows: noisy, uncomfortable, and power consuming.

    Besides, the automatic temperature control is not really "smooth" like in ordinary cars. When I turn on the AUTO mode, you either get frozen or steamed, alternatively. Quite unpleasant environment. It's not just me, I had a lot of complaints from passengers also.
    Is it that the temperature sensors in my M3 are defective or is it a glitch in the climate control design?
  • edited September 2019
    ezio, I understand you r complaint, but I answered your question in both respects. I never said it is an elegant solution. If you turn off the A/C and turn the temperature down to LOW, or below ambient, the heater won't come on. Then you just have to make sure re-circ is off too.

    Now for your "besides..." just like in other cars, and for HVAC in general, humidity matters, as does airflow on you and the passengers. 72 while on A/C is not the same as 72 on heat. I have to adjust the temperature the same as I did in my last "ordinary" car. The only exception is the stupid heater coming on when I don't want it to come on.
  • edited September 2019 Does anybody here even know who Rube Goldberg is/was?
  • edited September 2019
    I have had a couple other cars that have had "bad smell with A/C". Filter replacement and cleaning usually does the trick.

    But to prevent the problem from happening in the first place I learned to change to internal air-flow when the A/C is on. That way you're not dehumidifying/cooling a ton of air, just what's in the cabin and the humidity that seeps in. This greatly reduces condensation created by the A/C. It's also much more efficient.

    Some cars do this by default when you turn on the A/C, but some don't and M3 is one of those
  • edited September 2019
    Thanks derotam, I understand there is now way to have outside air ventilation without involving the temperature regulation, other cars do, M3 doesn't. I can live with that.

    The "besides" point is more tricky. I understand your point re. humidity and subjective perception with A/C on vs. A/C off.
    This is not the problem, trouble is experiencing wild temperature fluctuations while on AUTO mode.
    Unlike other cars, M3 alternatively blows chill wind so everybody freezes (when temperature is above the set temperature) AND furnace hot air so everybody sweats (when temperature is below the set temperature).

    Other cars don't have these extreme hot/cold fluctuations when in AUTO mode, they gently regulate airflow and air temperature so the car inside stays around the desired temperature.

    Therefore the question is: is it because of a defective sensor (that can be fixed) or is it a defective design of the HVAC system?
  • edited September 2019
    #syclone: Yep, probably gotta be 70 to know about Rube. More than 1 of us here.
  • edited September 2019
    ezio. But if you get in your car and set the temperature for the same as ambient, and in AUTO, you will have neither A/C nor Heat, and the fan speed will be low. If you adjust the temperature wildly, then you will get wild temperature swings in the air coming out of the vents.

    Now I will concur, in regards to winter time and heater usage, that because of the way the heater works and the way the human body feels airflow...that after the cabin gets up to set temp, the heater turn down too low, if on at all, which causes the air blowing in the cabin to feel cool. Air at the set point temperature(when heating is required in winter), will feel cool to the human body.

    In ordinary cars and in a very simplistic explanation, that have heat pumps, you have a hot water supply which is where the air blows across to give you your cabin heat...this maintains its temperature and the only thing that varies is the fan speed. This gives you "warm" air for your body to feel.

    In the winter time, I tend to set the set point higher, but then adjust the airflow so that it doesn't blow directly on me.

    The HVAC is designed as it is designed and is functioning as such. There are many ways to do things, and one way isn't necessarily "better" than another depending on the application.
  • edited November -1
    Hi derotam. Interesting discussion. I hope I'm not boring anyone out there :-)

    I can't explain myself clearly, so let me make an example.

    In my former car, a BMW X1, if I set the AUTO temperature to 24° C (75 °F) the inside of the car is kept somewhere between 23 and 25° (73-77), regardless of outside temperature, humidity or winter/summer subjective perception.
    The airflow provided by the car also is somewhere near the 25° set point ... you feel comfortable.

    Fast forward to M3, if I set AUTO temperature to 24°, at some point i get an air inflow of say 15° (59 F) and everybody's chilling, this cools the car, so that temperature will eventually go below 24°, at that point the fans start flooding with say 32° (90 F) and everybody's sweating ... after a while the car temperature will go over 24° and the chilling cycle will restart, and so on ... freeze-bake-freeze-bake.

    This is what I mean by wild fluctuations.
    People get annoyed and start complaining about how uncomfortable the M3 is ... reminds me of the old italian trains of the '80s :-)
  • edited November -1
    @syclone - yes, I've seen Mythbusters. ;)
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