I can’t fully explain why, but for whatever reason, certain air-cooled Porsches seem to have the most needlessly convoluted HVAC controls. This is surprising because, as far as HVAC systems tend to go, the ones in older air-cooled Porsches aren’t especially complicated. Like their air-cooled ancestors, Volkswagens, the heating and defrosting system is mostly just a series of cable-actuated flaps that guide and direct fresh air heated through the engine’s heat exchangers. It’s not exactly rocket science. And yet, somehow, I think Porsche managed to make, in the case of the heating and defrosting controls on the one-year-only 1976 Porsche 912E, the most convoluted and needlessly baffling defroster/defogger controls the world has ever seen.
I’m genuinely impressed by the achievement; I think the 912E is unique among all automobiles in that it has a windshield defroster setup that would, at least for a decent period of time, baffle almost any driver, from any point in automotive history and any part of the world, even accounting for translating the surprisingly ample amount of text involved in the controls. In our modern era of HVAC controls that tend to have dedicated windshield defrost buttons or positions on a dial or even icons on a touchscreen, this may seem hard to conceive, but I’m here to show you exactly what I mean, so you can feel the same awe and wonder that I do.
First, to fully appreciate the madness of the 912E’s defroster controls, let’s just get some control samples out of the way. We’ll start with how defrosting/defogging happens in a huge number of modern cars – and I’m being really generous with “modern” since this basic method started in earnest in the 1980s. This is the “three knob” method, one that uses one knob for fan speed, one for temperature, and one for where the air blows, as in on your face, feet, or directed at the windshield, to defrost/defog it. The little “snakes slithering up a fan” icon is normally used for this. Here is this basic setup, as seen on the Slate pickup:
Okay, so that’s a relatively modern way. You want to defrost the windshield, you crank the heat and fan, and turn the dial to the snakes on the windshield icon. Easy!
But let’s see what some setups closer to the 912E used, as in other maybe air-cooled car setups, because those were always, let’s be honest, a little weirder. My Citroën 2CV, for example, is a bit odd, but not really difficult. There’s one funny little lever for how much heated air is coming into the car, and then there’s a little ball-topped rod you pull or push depending on if you want that heated air directed to the cabin or 0nto the windshield:
The volume of heated air lever is the thing in the upper right, with the red and blue circles. Closer to red is more heated air, blue is just regular ambient air. Pull the black ball back for windshield defrosting, push it forward for cabin heat. It’s a bit odd, but pretty simple, really, and I’m using this as an example because, fundamentally, this is all that the 912E’s HVAC system is doing, too.
Let’s look at how a VW Beetle accomplishes the same thing, because it’s similar:
In the Beetle’s case, there’s one lever between the seats for the volume of heat coming into the car, and another lever between the seats to direct that air to either the vents by the windshield or on the floor of the cabin. Really, the same thing as the 2CV, just with a different placement of levers. If we look at the more up-market VW Type 4, the car that actually donated its engine for use in the Porsche 912E, we see a bit more complexity, but mostly just because the Type 4 has a more advanced fresh-air ventilation system and an auxiliary gas heater with such nifty features as a timer you can use to pre-heat the car on cold mornings.
Even so, the basics of windshield defrosting aren’t really different than in a Beetle:
Looking past all the ventilation and gas heater stuff, if you want hot air to melt frost or clear fog from your windshield, you’re still pushing that DEF/HEAT lever to the DEF setting. That’s pretty much it!
Okay, so we’ve seen what these close siblings to the 912E ask of you if you want your windshield defrosted; let’s see what the 912E herself demands:
Wait. What? This is the part that gets me:
“DEFROST: MOVE UPPER LEVERS LEFT, LOWER LEVER RIGHT.”
Something about that sentence just takes a moment to process, at least for me. If I was driving and having trouble seeing out of my windshield, I don’t think I’d be able to grok it any quicker?
Okay. So, the red lever – which I think is for the volume of heated air coming in, which is sort of like temperature, in that it mixes with ambient air, in this case needs to get cranked all the way up to full heat, because it’s the lower lever, and the upper two levers both go all the way left? Okay, but that seems to mean the fan gets turned off, which I don’t understand why that would be, and then that makes me realize I don’t really know if it’s the middle lever that controls the fan or the top one, and whichever one it is, I’m not clear on what the other lever does?
Is the middle lever like the defroster/cabin slider? I think it may be, though the markings and position all make it more confusing. There are up and down arrows at each end of these right-to-left sliders, and I think it’s DEF.MAX on the right and DEF.MIN on the left, but if that’s the case, then why would I be told by that sentence to move the upper levers to the far left? Wouldn’t I want the slider to DEF:MAX for maximum defrostery?
Or is the bottom lever, the red one that suggests heat, the defrost max/min lever? Because then at least I’d be told to slide that to DEF:MAX, which makes a bit more sense? But then what does the middle lever do?
This all feels like someone way overthought this to the point of madness. It shouldn’t be this hard! And here’s the amazing thing: Porsche seems to have kept this baffling system for quite a while: the same basic setup is used on 1980s Porsche 911s, just augmented with other air-conditioning controls and the traditional between-the-seats heat/defroster levers. This guy seems delighted to show you the weirdness of it all:
I think the 911 implementation of the strange 3-slider setup is less bad than the 912E because it (A) eliminates the confusing sentence and (II) it can be mostly ignored because of the other sets of A/C and heat/defrost controls? Still, it’s hilariously obtuse.
Now Porsche isn’t the only carmaker that has managed to make defrosting strangely difficult; look at what the Fiat Brava asks you to do before you can defrost your windshield:
The Fiat asks that you close the central heater outlets your own damn self so the air can get re-directed to the windshield. It doesn’t really have any separate defroster controls at all, just six words that tell you how to make defrosting happen. That feels pretty lazy, but at least it’s pretty straightforward.
The Fiat’s cousin, the Alfa Romeo GTV6, is sort of similar; while it has a setting for defroster (slider all the way to the right, by the universal snakes-on-a-fan icon), it also takes the time to note that if you want MAX DEF (which I think just means either the defroster actually doing something or, less likely, Mos Def’s older brother) then you need to close those two central vents yourself.
A slight step up from the Brava, still not great, but still fundamentally understandable.
Either way, these are both a million BTUs better than the Porsche 912E setup which, I’ll be honest with you, I’m still not entirely sure I understand. If we have any 912E owners reading this, I’d love to know more: how exactly do you get your windshield defrosted? I really like 912s, even the odd US-market-only, one-year-only, VW-engined 912E, so please don’t consider this a slight. If I had a 912E, the baffling HVAC controls would be one of my favorite parts of the car, and I’d ask everyone I gave a ride to please, if they wouldn’t mind, turning on my windshield defroster, just so I could witness that delicious moment of perplexity and confusion.
I bet it’s really satisfying to see.
I love it, feels like a minigame 🙂 People complain about low driver involvement nowadays, this is part of the experience.
Reading through the comments I am alarmed that there are some 911 owners that apparently don’t know that one of the two knobs between the seats controls the heater, and the other controls the throttle.
The problem is that the main heater control is on the floor next to the shift lever. It controls the flaps to the exhaust headers. Air you looking at a picture or at an actual car? It’s pretty simple other that the fact that they are so often broken.
I think the 912e and 911s of that era had a heater blower on the back with the engine and the heat source. There was another motor in the front for the defrost and the AC. This made sense, because the windshield and the AC evaporator and condenser would be in the front. AC was still sort of a weird American thing then, but running the air through the AC to dry it and mixing it with hot air would be as close to the way a water cooled car would do it. I don’t think Porsche was mad enough to send cooled air back to the exhaust pipes and forward to the windshield to heat the cool dry air like everyone else.
This is all a hazy memory, my Porsche when it ran had no heat or defrost at all because the exhaust headers had no provision for heating.
I had an air-cooled 911 that I loved dearly even thought it almost killed me when I once lightly touched the brakes in the rain. Anyway, I remember pulling out the owners manual to learn and immediately forget how to operate those dash levers at least a dozen times. This particular car also had an option called “Automatic Heating Control” that added a black knob down between the seats with no markings to indicate what it would do. I viewed it with suspicion and never touched it.
The black knob was the idle speed control to set the idle fast since Weber carbs have no chokes. You could also use it as a hand throttle if your leg cramped up on a cross country trip. The Red knob would open the flap to send air through the head exchange on the exhaust headers. The 1970 911 and 914/6 were like that. The four cylinder 914 had fuel injection, so no black hand throttle, and only the red knob
Hmm, I think you just don’t drive it in the winter.
By now any GTV6 has ventilated itself….
I’d be curious what the heater controls were like in the first gen 912s.
Are the heat exchangers in these air-cooled engine cars prone to developing leaks?
In the Cessna 150 I shared with three other co-owners, we would put little stick-on CO detectors on the dash every three or four months to make sure any leaks were detected before discovering it some other (probably unpleasant) way.
My grandfather’s 67 912 had a flap knob on the floor and fan speed and defrost or heat but not both at once levers on the dash. The Mercedes was about the same but each side got its own set of controls.
At least CO poisoning would be nice and peaceful for the people in the plane.
Probably terrifying for witnesses, though.
In one low oxygen case, a fit non pilot was the last conscious person on the plane.
They ran out of fuel before he was able to find a radio channel to communicate.
It’s like the old joke: When I die, I want to go peacefully like my grandfather did–in his sleep. Not yelling and screaming like the passengers in his car.
Hypoxia is far more subtle and dangerous than even the pilot cautions indicate.
If you have a friend experiencing it, you can’t be too proactive.
There is suspicion you might experience a degree in poorly ventilated buildings.
An oxygen saturation tester for your finger is not a bad idea.
To me this makes perfect sense. You have the heat coming and you are just portioning out the heat between windshield and passenger. I think you as a car journalist are over thinking it as you should. I don’t overthink much because I don’t need to have the ICE motor explained to start and drive. The transmission to change gears since now automatic. I think you mentioned your CV2 was quite similar and if I’m not mistaken it doesn’t have any directions on the dashboard at all just pictures that are a bit hard to understand
I found an owners’ manual for an early enough 911:
The way it’s described in the manual makes it a bit clearer to me – the heating and ventilation systems are controlled separately. That said, there is still a lever next to the handbrake to control how much hot air is sent to the dash.
Anyway, if there was space on the dash it would probably say
“Push the top lever all the way to the left to stop cold air entering the car through the ventilation system. Push the middle lever all the way to the left to close the flap that allows cold air through the windscreen vents, and then push the lower lever all the way to the right to direct hot air to the windscreen.”
To be fair, Germans had all been doing it like that for decades. Just like Americans controlling the headlights with their feet.
German engineers get a bad rep. They Knew any usable heat from an air cooled engine heat exchangers in freezing temperatures was merely a suggestion, and the best way to warm occupants was to amp up frustration, physical thrashing, and head steaming.
( my 71 Karmann Ghia Conv., friends 72?bus, 912E that came into the shop, granted my KG was rotted out, and replaced with 4 outlet Monza exhaust that eliminated the shot exchangers)
The Mercedes W116 sedan (water cooled) with manual HVAC controls has a setup as confusing as this Porsche one.
https://tse4.mm.bing.net/th/id/OIP.ZAsK3N9mG11KvYa9AaXkoAHaFj?r=0&rs=1&pid=ImgDetMain&o=7&rm=3
Yes! I had one of those and was initially totally baffled by the controls.
I recall studying the ventilation section of the owner’s manual on a borrowed 2007 MB (but Dodge branded) Sprinter van before taking a long trip. I was amazed at the oddball complexity in a relatively modern vehicle!
“If we have any 912E owners reading this, I’d love to know more: how exactly do you get your windshield defrosted?”
One of the editors or writers (Bradley Brownell, IIRC) over at the German lighting site has a 912E. Any chance of getting a hold of that 912E or at least its owner? Dunno if the schism between the two websites is on par with the bishops of the Society of St Pius X squabbling with the Vatican, tho… (yeah, despite being atheist for many decades I was raised Catholic so I’ve been eating plenty of popcorn while following the latest schism news, lol.)
Yeah it’s the diet of Worms all over again.
For that matter, fourth century Christianity is pretty wild before the Romans decided to take over. Schisms all over the place.
I too was raised Christian, went atheist, then married into a Jewish family, which is my comfort zone now.
I’d probably hitch up with Ethical Culture, sort of like Unitarians but Jewish, but I don’t really feel the need.
Which lighting site?
I’m going to have a go at this, but these are memories from helping a neighbour work this all out in the 1980s. The top two sliders control ambient (outside) air. The top slider controls a fan for ambient air only. The middle slider controls whether ambient air goes up or down. The bottom slider controls whether heated air from the engine goes up or down. Two levers by the seats control how much hot air enters the car (left/right side) using a fan in the engine compartment. So the reason that the top two sliders need to be to the left when defrosting is that you’re minimising ambient air and maximising heated air, the volume of which is controlled from between the seats, not from the three sliders. Cars with air conditioning have yet another set of dials on the console. This all said, the only thing that actually seemed to do anything were the two heat levers between the seats. Everything else created different levels of noise but not much action.
I think one of these measures if the air is directed at the windshield or heat vent.
One of the levers on the floor controls the hot air*, the other is a hand throttle.
*or oil mist and exhaust.
I loathe that modern defrosters force recirc off. I don’t want the diesel exhaust, paper mill, skunk, or landfill smell in my car and I don’t really care if it takes a few seconds longer to clear my view. Frankly, I hate it so much I allow my window to become way to obscured before I finally relent. My 2008 Civic was the last vehicle where I as the operator could control this function. It would automatically turn off recirc, but I could punch the button and turn it back on; it got to be muscle memory. Now big HVAC controls the horizontal and the vertical to.
My 98 Dodge has a button added that turns power to the compressor on or off.
You can add a lot more options where it matters.
Well you can always wait until the windshield is defrosted before you drive. That was my preference until I bought a truck with diesel motor that allowed me to plug my block heater to my porch light and have warm air for the defroster and driver immediately even at 10 below at 3am
I’m the opposite with my GR86. For whatever reason, the computer defaults to recirc whenever it’s warm outside on startup and whenever it feels like it during a drive. The interior is small, so if I’ve got the windows up and the vent isn’t open, it gets stuffy rather quickly. I’ll be driving along when, all of a sudden I’m uncomfortable and the windshield is fogging, so I look over and, sure enough, it’s on recirc and I’m unleashing a string of obscenities and curses against the lineages of the world’s computer programmers. Again. Another reason an actual mechanical switch is superior—whatever it’s set at, it stays at.
My 2010 Prius has a button for recirculating air. On or off, which isn’t quite optimal either.
My Fords are too eager to force recirc on, I usually don’t want it. At least there is a toggle button, but let ME decide when recirc turns on.
So my 1979 911 has the same unit and every time it gets cold i have to youtube how to make it blow hot air where i want it. Something about how it operates just leaves my head as soon as i get it to work. I also have the lovely levers down between the seats too.
My dad had a mid-’70s Fiat 124 Convertible that I learned to drive stick on, and it had the most confusing climate controls. 3 levers that each did something, and a rocker switch for the fan. What made it crazy was that they were down in the center between the seats, on either side of the parking brake. So, if you looked down there to try to puzzle out which lever did which you were pretty much guaranteed to crash. There was no A/C, so to this day I am not sure what those controls did. You would just flip the fan switch and then play with the levers while putting your hands by the vents until you were happy. Love that Italian design!!!
I don’t believe the Fiat convertible was too concerned about defrost in a convertible.
Unless you had air, it’s heat on, heat off, same for fan.
My first Fiat had dash top rotating vents, a very superior feature.
If I redo a dash, I’m going to add that feature! Especially brilliant with a rear camera screen taking up real estate.
This is not a one-year only thing for just the 912 as your post implies – This was standard on every 911 derivative up through 1989.
It was only with the advent of the 1990 964 models that the HVAC controls were updated.
There are aftermarket kits which one can update the old controls to a more modern setup.
Not just Porsches. Vanagons have a similar setup but more complex with four sliders and two fans. Plus the early vans have two dash vents that are just forced fresh air with no connection to the rest of the HVAC system and two air exit vents on the bottom of the front doors – all with their own controls.
https://gowesty.com/blogs/article-library/ventilation-heat-and-a-c-in-the-vanagon-explained?srsltid=AfmBOoolsSRyPodOVzdM8PDMcGdsf2h12YOLx2YJ3rW4NWhkfiGUdmPV
This is aside from your point, but wouldn’t it be ironic if all we had to do to fix climate change was get in our cars all at once, start them up, set our climate controls to cool and open the doors?
I like the idea.
All we need to do is shut down daylight savings time.
That extra hour of sunshine is the problem!
That’s a terrible idea. If you’re overheating, you have to roll down the windows and run the heater, not the A/C.
That how I kept my Oldsmobile alive in traffic! I don’t miss that part.
I added an electric fan with a switch under the dash
The AC usually turns on a second fan, which can be helpful if the overheating is due to lack of airflow, like in traffic. You can also run the AC with the heat on (or just use defrost and the hot setting as the AC should run). If you have coolant and oil temp gauges, it’s interesting (or maybe that’s just me) to see the differences in temps under different conditions and settings. To my surprise, in traffic, I’ve found AC to be more effective in reducing temps than blasting heat, I assume due to the greater airflow of the added fan and slow water pump speeds (at least with a car that has nothing wrong with the cooling system). Of course, when I had cars with overheating issues, they didn’t have AC.
My Toyota defaults to constant engine fans in AC mode, so that can help stay cooler.
Did that one time on the first chilly fall morning. Engine temps started climbing even higher after I cranked the heat. Turns out the valve to the heater core broke, so when I blasted the heater it just sent more coolant through the valve and onto the street.
I always thought having AC which removes heat from the air and puts the cold air inside and the now really hot air outside in the summer made for hotter summer and heat pumps doing the reverse made winter colder. But what do I know
Dammit, that makes too much sense.
914s have a similar dash arrangement plus another lever between the seats to control the heat exchanger flaps. Also, moving that center level (between the seats) to full “on” activates a separate heater blower.
Yeah, it was confusing at first but after using it a few times it was no big deal.
Oh how far we have come. Modern innovation:
Stab, I said stab, touchscreen
Stab ‘car’ icon. Stab again
OK now stab ‘setting’ icon
Stab climate ‘icon’
Stab again, oops, hit a bump, stab ‘back’
Stab ‘left’, ‘right’, ‘front’ or ‘rear’ motorized vent icon
Stab ‘defrost’
Stab ‘defrost’ again, oops hit a bump, stab ‘back’, oh no, not home screen!
Start over
And so on…
Most people assumed Porsche drivers lost control and crashed their cars because of the rear-engine design and difficulty to drive at the limit.
Nope.
They were trying to figure out the HVAC.
Now that’s funny I don’t care who you are. Lol
I think either the knobs are missing on my Bug’s heater levers, or they’re worn out, because I didn’t realize they both did different things!
I had one in high school and also never knew. All those Pacific Northwest morning where I just kept a squeegee and a rag to wipe off fog on the windshield, this would have been good information to have!
After this engineer was done setting up defroster controls on the 912, he went on in the 2000’s to handle directional signs to get to ground transportation at LaGuardia.
My E39 turns the heat up full blast when you punch the defrost button. Want to defog with cool dry air in the summer? Nope. Full hot. I don’t know if it’s designed that way, or just broken.
It has dual zone climate control, but then there’s a slider that controls the temperature for the center vent and side window vents independently from the other vents. So you can have heat, but cold air on your face, or vice versa. Apparently that’s a BMW thing.
Serves you right for buying a furrin car.lol
Jason.. my E28 BMW has the same “strategy” but instead of written instructions it has a little tiny diagram that you are supposed to put the top on the right (open) and two bottoms on the left (closed).
I guess before hvac systems had electronic dampers tha twas the way to direct air….
oh yeah also E28 never blows hot air in the center/face vents to “avoid fatigue” LMAO so in the Canadain winter here my hands are always freezing and my feet are sweating
E30 as well.
Electronic now? Not pneumatic?
Pretty sure most aircooled 911s are like this, not just the 912.
Boy do I have an infographic you need to add to this post.
https://i.imgur.com/XV7HUCB.jpeg
I have owned my 77 911 since 2013, and I still have no idea how it works, lmao
And it got even worse as the years went by! My ’97’s graphic layout is mostly white on black monochromatic, so the sliders are super confusing as to what they do, and what they do differently than each other. And the a/c’s snowflake icon always makes me think it’s the defroster.
The snowflake symbol signifies how special Porsche drivers are.
I like how the one comment is “does one still need a university degree to operate Porsches?”