1964 Cadillac Comfort Control
Most cars today are equipped with (or at least have available as an option) some form of automatic climate control, where you set the desired temperature, press auto, and it does the rest.
Automatic climate control was rarely seen when I was growing up, and on the few occasions I did see a car so equipped it always struck me as being a bit of black magic, the way it changed the fan speed, temperature, and air direction all on its own. Residential heating and cooling systems, by contrast, are exceedingly simple, with just a basic thermostat to cycle the system on and off as needed. So where did these systems come from, and how long have they been around?
Cadillac released Comfort Control, the world’s first fully automatic climate control system in 1964. This system is an amazing accomplishment and a reminder of how GM and Cadillac really once were the standard of the world. Let’s take a quick look at the development and workings of this system.
The obstacles to bringing Comfort Control to market were daunting. First up was the problem of airflow. Most early A/C systems looked similar to the diagram above. Other than a common blower, the heating and air conditioning systems were essentially separate, with the heat blowing out the floor and defroster, while the A/C blew out its own dedicated panel outlets. Remember how cars without A/C used to not come with panel vents? This is why. This approach also made it easy to add air conditioning to a car later: A/C was often available as both a factory- and dealer-installed option in its early years. (See here for a quick refresher on the history of automotive A/C).
Early attempts by GM to automate this setup performed poorly: Relying on a shutoff valve to control the hot water and a bypass valve to control the evaporator made the temperature of both difficult to modulate and slow to change. Humidity was also difficult to control with the heated air bypassing the A/C evaporator.
The insight that solved this was the idea of blending the hot and cold air together. All incoming air is first passed through the evaporator where it was cooled and dehumidified. Then warm air could be reintroduced using a blend door on the heater core, if warmer air is called for. This blended air could then be sent to any outlet: Floor, panel, or defrost (or in some systems, one or more combinations of these). Temperature changes in this setup are effective almost immediately since you no longer have to wait for the thermal mass of the evaporator or heater core to change. This is how virtually every modern automotive HVAC system, automatic or manual, works today.
With the airflow problem solved, GM now had to solve the problem of control. While modern climate control systems use microprocessors and electronic actuators to work their magic, the Cadillac Comfort Control is pure analog.
Temperature sensing is accomplished via three thermistors (thermal resistors) – one for outside temperature, one for inside, and one for duct temperature. The purpose of the duct temperature sensor is to compensate for variations in heat and air conditioning production due to variations in engine temperature and speed. However, these three thermistors are not treated as three separate inputs, as multi-channel control systems were expensive and complicated in the 1960s, and this system needed to be simple, inexpensive, and reliable. Instead, these three thermistors are wired in series into a resistor string (along with the rheostat on the temperature control dial), essentially summing their values into a single signal.
It is hard to believe that a large variety of behaviors (recirculate/fresh air blend, temperature blend door, outlet direction blend door, coolant shutoff valve, and blower speed) can be controlled by a single input, but you can see how they mapped the various output states to a single input in the function diagram above. High temperature readings on all the thermistors would push the function map all the way to the right, triggering various behaviors like switching the inlet from fresh air to recirculate and closing the coolant shutoff valve. Low readings from all the thermistors would correspondingly push the function map all the way to the other side. Intermediate temperatures and combinations of temperatures (e.g. high interior temperature and low exterior temperature) would push it somewhere to the middle.
So how was this “program” implemented without digital electronics? Simple. With a single two-transistor amplifier (to boost the signal), a single vacuum transducer (to convert the electrical signal into a vacuum signal), and a circuit board. You can literally see the blower speed control from the earlier diagram “hardcoded” on the PCB pictured above, while vacuum actuators and cams handled the airflow doors in a similar manner. Genius!
This single-channel analog control feedback system is the template that pretty much all subsequent electro-mechanical automatic climate control systems would follow, up until the introduction of digital systems in the 1980s.
1964 Cadillac Comfort Control
Cadillac introduced Comfort Control in 1964 as a $495 ($4,100 in 2020) option. Amazingly, all this technology represented just a $21 increase over the $474 price of the manual 1963 A/C option. Cadillac felt confident enough in this system that Comfort Control was the only air conditioning system available in 1964 – no manual system was offered. In fact, Cadillac would only offer automatic climate control after 1964 (optional at first, and then standard starting in the 1970s). As near as I can tell, manual A/C wouldn’t appear again in a Cadillac until the 1981 Cimarron.
1964 Cadillac Comfort Control Dealer Guide
At first glance, the controls for this first generation Comfort Control system look deceptively simple with only two modes (three, if you count “Off”). No doubt this was at the behest of the marketers, who would have wanted the system to appear as simple and intelligent as possible. In actuality, adjusting the slider to the right Automatic detent would have boosted the fan speed, and the rightmost defrost marking was actually a deice setting (with all the air going through the defroster ducts), as explained in the brochure above. Later iterations of this system would make the operation of the various detents more clear with better labeling of the controls.
Comfort Control wouldn’t stay a Cadillac exclusive for long. Pontiac got automatic climate control the very next model year, in 1965. Or at least that is what the 1965 brochure says. The take rate in 1965 for this option must have been extremely low, as my Google image searches for a 1965 Pontiac so equipped came back empty.
1966 Lincoln Continental Automatic Temperature Control
Lincoln would introduce its first automatic temperature control in the 1966 Continental. It offered the same degree of manual control as the Cadillac Comfort Control system, but the operation was a little more discoverable due to the use of buttons instead of a slider. Unlike Cadillac, Lincoln continued to offer a manual air conditioner as a less expensive alternative to the fully automatic system and would continue to do so for many years.
1966 Oldsmobile Comfortron shown in 1966 Toronado
Oldsmobile would get their own version of Cadillac’s automatic climate control in 1966, called Comfortron, initially available in the Toronado and Ninety-Eight. The Buick LeSabre, Wildcat, and Electra would get this system as an option starting in 1967.
1967 Cadillac Automatic Climate Control
Not to be outdone, Cadillac introduced their second generation automatic climate control system (no longer branded Comfort Control) in 1967, which offered more intuitive controls and a greater degree of manual overrides than the first generation Comfort Control.
1968 Imperial Auto-Temp
Chrysler would finally join the automatic climate control ranks with the introduction of their Auto-Temp system in 1968. It was available on all Chrysler and Imperial models that year. Supposedly it was available late in the 1967 model year, but I was unable to find any 1967 models so equipped.
1966 Chevrolet Caprice Comfortron
Much like manual air conditioning did in the late 50s, it didn’t take long for automatic climate control to trickle down from the higher brands to the lower brands. The Chevrolet Caprice got Comfortron in 1966, and the 1968 Thunderbird would be the first Ford branded car to get ATC (although it would be 1971 before it showed up in any Mercury). Still, ATC would be a rare sight in the entry-level brands for decades to come.
Chrysler introduced their second generation Auto-Temp II system in 1971. It replaced vacuum actuators with electromechanical servos, but otherwise still operated under the same principles of all the other single-channel analog systems.
1976 Mercedes Benz Automatic Climate Control
Many European automakers relied on US automakers for their air conditioning systems in the 1960s and 1970s. Mercedes-Benz was no different, and they released their first ATC system in 1976, using components from a variety of US automakers. The controller was a Chrysler Auto-Temp II unit (the high- and low-auto settings are a dead giveaway), while the compressor was a GM Harrison unit.
1980 Cadillac Eldorado Dashboard
As late as 1979, every ATC system still operated under the same basic principles as the OG 1964 Cadillac Comfort Control introduced 15 years earlier. That would change in 1980, when Cadillac went digital in a big way, introducing the world’s first fully electronic automatic climate control system on the Eldorado and Seville. Modern automatic climate control had finally arrived.
So where did automotive air conditioning go from here? Follow the link for dual-zone automatic climate control.
Great piece! I spent my first years out of engineering school working and designing commercial HVAC automatic control systems in the late 80’s. Company was appropriately named ATC Systems. They used analog pneumatic receiver controllers, actuators and temp/humidity sensors and worked similar to these automobile systems to modulate the airflow, start/ modulate the compressor and hot water supply Mainly four sensors, outdoor air, discharge air, mixed air and return or room temps. A real bear to keep the control air in the lines clean but they worked and were pretty inexpensive. Also came across a few old systems with vacuum tube amps! Can’t wait to read the next installment.
A/C was so uncommon in Uruguay, be it for home use or cars, that each and every installation was interesting. At first only banks and cinemas had it, and the window installed equipment was frequent but really expensive. My dad had one in his doctor’s office, but only in his own office. The waitin room, the X-ray room, the ECG room…or relied on fans.
Some friends of my Dad had A/C in their upscale cars, upscale meaning usually a low price American brand; an Impala with PS PB PG AC and PW in 1968 was worth a small fortune here. Or not so small. Car AC began to trickle down from imported cars to locals in 1978, when Argentinian Falcons began to have it as an option. Being American modeled, the equipment was great. Some Opel Rekords were also equipped with factory AC, which didn´’t work at all, absolutely insufficient, expensive and inefficient. In 1980 imports were allowed for the general public, and smaller European and Japanese cars began to appear, and Japanese usually had AC as a very expensive option which worked very well. A friend of mine got for his 18th birthday a brand new Honda Civic in 1982 with AC (from a rich grandpa). Fantastic. Finally, around 2005 or so, AC began to be a common feature and now there are almost no cars that come without it. But I can easily remember the time when even upmarket cars would only drive with their windows open in 100F weather.
Thanks much Tom for your great series.
I like the thermostat in my home. But even though it’s a “smart” Nest device and our furnace has a variable speed blower, it still often seems to struggle to get the rate heating up a cold house balanced with blower noise. So a better climate control would be nice at home. In my car, I have never seen the need and in the last few cars I’ve owned with ATC I never use it. What could be easier than twiddling a few knobs or buttons within arm’s reach? I’m not a total Luddite … I like my power windows, traction control, Bluetooth, etc. my daily driver has even been an automatic for the last 6 years. But I’ll adjust my own temperature, fan speed and air direction, thank you. And on both of our Toyota’s and the Forester the automatic control often had a mind of its own, suddenly raising fan speed or turning on recirc when it didn’t seem necessary.
The only car that’s ever had ATC was my Mom’s 1987 Deville. Darned thing broke twice in the year I owned it, with a $1,500 bill the first time. The next time the AC broke, I traded the car for a 2005 Sentra SE-R Spec V.
Oh look that 77 New Yorker has Auto-Temp I. Great. Oh, and that New Yorker has Auto-Temp II. Not so great today.
In practice, I don’t think auto temperature control works very well. I’d rather just control everything directly. Given solar insolation, the effect of clothes, and drafts, there are too many variables for an automatic system to effectively gauge what is required at any moment.
just an example of the unnecessary complexity that automakers seem to gravitate to.
My experience has been mixed — the auto. temperature control on our former 2006 Crown Victoria never worked well. On our 1995 Thunderbird, it used to work good, but now is somewhat iffy, so I just use it on manual mode anymore.
However, our 2010 Honda Odyssey has auto. temperature control that works excellently… never had any problems. Oddly, our newest car, a 2018 Kia Sedona just has manual a/c, and I don’t miss having automatic climate control all that much.
This has been a great topic. Thanks, Tom!
My Dad’s first Cadillac, and our first air-conditioned car, was a 1963 Sixty-Two. It had manual air conditioning…A/C itself was an option…so we missed automatic control by a year. His first with automatic A/C was a 1966 DeVille. He was unsatisfied with it at first, always running it at high fan speed and minimum temp, which went down to 65F…and this was in relatively cool San Francisco. Still it did not seem as cold as the manual system in the 1963. The rotation of the temperature control dial was asymmetric, which seemed odd. We determined that there was an adjustment for that; you slid a special, thin wrench alongside the dial to engage its shaft and hold it, and then moved the dial as desired — it was a friction fit and would slide on the shaft. Fixed.
I still have only manual A/C in my cars, or in the case of one, no A/C. Who bought A/C in a non-luxury convertible in 1963?
My experience with ATC in older cars has been, well, not great. The 84 Olds (a relatively simple system) never provided cold a/c air in automatic mode until I had the Olds dealer replace the programmer box.
The 89 Cadillac would randomly refuse to start the blower in cold weather unless it was set to defrost. And the 77 Chrysler was usually decent until one really, really cold day when the temp coming from the heat ducts got progressively cooler and cooler as an hour-long highway trip progressed.
When I have had it in (temporary) newer cars I tend to “set it and forget it”. So I like it when it works and HATE HATE HATE it when it doesn’t. Thus I am not sad that none of my current cars has it.
Your opening shot is giving me some nasty flashbacks – I spent many frenzied moments fooling with a wiper switch just like that on my 63 Cadillac trying to get wipers to either start or turn off – which they were extremely reluctant to do whenever the interior of the car was cold.
JP, I had the same system in my Olds Custom Cruiser. It never work right from day 1. I had the old work orders from when the car was new and it was in the shop a few times under warranty for lack of heat. When I got the car I had problems with the vacuum actuators. They weren’t cheap to buy from GM, so eventually I just converted it to a manual control. It worked far better as a manual system.
I agree, I hate when the modern systems don’t work well. Many of the cars I drive at work have it, and I am rarely satisfied with the performance. None of my own cars have it. I much prefer manual controlled systems.
BTW, good write-up Tom!
Thanks for another installment in the series. Can you pinpoint when the temperature dial first appeared? Based on the article it is the 1971 Chrysler Auto Temp II but you don;t specifically say. I’m guessing tomorrow will get us into multi zone systems and possibly heat pumps since I think some electric cars use them.
I’ve owned 2 Buicks, 3 Lincolns and 1 Toyota equipped with automatic “climate control” factory air conditioning systems.
All 4 took longer to cool down the car’s interior here in usually hot and always humid New Orleans than a manual control factory A/C system did.
None of the 4 would get down to the vent output temperature that a manual control system would.
Looking forward to your next installment, Tom.
All of your A/C articles have been clear, concise and easily understandable.
Even my non-automotive sister could understand your great wealth of information!
All of your A/C articles have been clear, concise and easily understandable.
And cool! 🙂
Thank you for sharing this Tom.
I used to own a 2002 Chrysler T&C minivan with 3 zone ATC. On the center stack there were sensors underneath the vents. According to my manual these would actually scan your skin temperature and adjust the the heat/AC. I always wondered how that worked. That seemed like overkill to me too.
This is a great overview, as always. All of the cars I’ve personally owned with ACC have been new enough that they’ve been computer controlled, and I have to say they’ve been a mixed bag. My ’85 Conquest had an excellent system that was virtually “set it and forget it”, except when the head control unit in the dash needed replacement, which was an absurdly expensive proposition. I had 3 different Saab models with auto climate control and they were adequate. The best of the bunch was a ’93 9000, but that system was notorious for glitches, as as much as I liked it when it was working, I lived in constant fear of a blend door actuator problem, since that repair could be a nightmare. More recently the Chrysler systems I’ve had were just OK.
The most annoying thing about auto units is riding with people who don’t grasp the concept of what a thermostat is supposed to do. My other half is one who gets cold or hot and constantly adjusts temperature and.or fan speed. Like annoyingly constantly. I just can’t get the concept through to him that if you set the friggin’ thing at 72 degrees it’ll eventually get to that temperature and you’ll be comfortable.
In my 2007 VW, although it will get to the selected temp eventually, it does seem to reach it faster if set to max cold or max hot at first.
Thanks for the clear description of the elegant analog circuit, using the properties of the thermistors to create ‘logic’. This type of elegance was rather rare in American electronics but common in British and Russian ckts. Most American analog processors were more brute-forcish.
The inventor deserves credit, so I looked up the relevant patent. It’s 3,263,739, by George Gaskill.
https://patents.google.com/patent/US3263739A
I had an 1967 Imperial Crown 4dr hardtop with Auto Temp 1.. Wish it was a standard A/C…
My other favorite climate control – the Tempmatic in Pap’s 83 Oldsmobile 98 Regency. I remember the Automatic Climate Control in the 74 Sedan deVille – and of course all of my Cadillacs have Electronic Climate Control – all stuff I took for granted until riding in other lesser cars. The ECC panel came out just in time for the DFI cars to be used as the diagnostic panel – OFF+WARM buttons worked the same on my 84 SdV as on my 93 Brougham or my 95 Deville – GM really made sure to get their monies worth out of that system!
Great series Tom…looking forward to the ECC installment.
My dad ordered ACC on his 1977 Bonneville Brougham – actually it was only a semi-automatic system; you still had to control the fan speed and which air ducts to use manually, only the temperature control was automatic. Unfortunately, it worked terribly. The temperature sensor was on top of the dashboard, so of course it got easily fooled when the sun was beating down on it and it delivered frosty air. We wound up controlling the temperature manually, and it was frustrating cause it had a mind of its own. He stuck with manual A/C for the next several cars.
He finally got ACC with his ’95 Buick Park Avenue, which not only had a fully automatic system, but also allowed the relationship-saver feature that allowed the passenger to select a different temperature than the driver. On new cars there’s usually a separate digital display for each person, sometimes in back too. But on the ’91-’96 Park Ave, the passenger merely selected up to five degrees plus or minus from the main setting. But the control for this sure looked cool, on the passenger door panel, with one to five blue or red lights depending on how many times you tapped the red or blue warmer/cooler buttons. This system did an excellent job holding the selected temperatures. I suspect dual temp controls will be covered in the next installment.
Our first car with ACC was a 79 Colony Park. It (the ACC) sucked. It was horrible. There was only 1 sensor mounted above the glove box. Enough said.
Our second car with ACC was a ’98 Park Avenue. Worked great. Never a problem though each different servo made its own “insect noise” (for lack of a better term). I could tell what was going to happen next just by listening to it.
Our current ’03 Park Avenue ACC has operated perfectly and quietly all of these years. Have never even had to add refrigerant (knock on wood).
Knock on fake wood, right?
Had auto a/c in my ‘83 Buick Lesabre Broughm Limited. I was very expensive! And just as temperamental as the rest of the car. When it worked, it worked fine. But if it felt like it wanted to just send ice cold air onto your legs for the next 28 days then so be it. So I always preferred the manual air in my pick ups and farm equipment. It always worked on My cycle lol
Yep. but never too hard!
In my early ’80s Chevy, the AC controls seemed easy, and it blew cold air.
In my K-car, you pushed an AC button that seemed to activate a compressor (you could hear it and feel its vibration), then you would set the temperature you wanted and the system would take over.
I await tomorrow’s installment to see how these things really worked!
The article mentions Pontiac introducing ATC in 1965, but that the take rate may have been low. I also have not found any examples of ’65 Pontiacs online with ATC installed.
But I would know one if I saw it, as I once had a ’65 Pontiac Star Chief with ATC. Directly in front of the steering wheel, on the upper dash, was a rather large grill and binnacle that contained the cabin air sensor. If I’m not mistaken, this was essentially an auxiliary return air port, provided for sampling cabin air temperature. The ATC dash controls resembled the Pontiac radio, flanked on either side by chrome knobs, with the manual and automatic control buttons resembling radio station presets.
The system on my Star Chief worked marginally well…as long as the system held refrigerant. It had a slow leak I never found. It also soon after I entered the summer cooling season developed a balky directional damper, stubbornly blowing conditioned air out of the heater outlets on the floor. I fixed that by threading a coat hanger through the duct to nudge the damper where I wanted the air to go, but at a loss to automatic control.
I was always curious as to the control sequence for GM ATC; thanks for the enlightenment!
No one has mentioned the best part of an ATC system: the fact that, in cold weather, with the system set to “AUTO”, the fan will not start blowing until the engine temperature is sufficient to provide warm air.
Having lived my entire life in the northern part of the country, I always found this feature very nice, although I understand those who prefer manual control.
It’s not a part of auto climate control, it’s from another feature, basically delaying the air from coming out until it reaches certain temperature. Early GM units didn’t have it
Great stuff, Mr H.
As has been noted above, you’ve a fine knack for making this rather mysterious stuff understandable. The presence of such articles is one of the unique gems of this site.
May the wind be always at your back.
(Well, your face in this case, but you know what I mean).
Great essay and I like everyone ’s comments. I have had ATV equipped cars since 2000. I never use it. I prefer to make my own selection when I use the A/C. When driving alone I will most often opt for open windows (no, I do not want icing glass side curtains🤗).
The GM supplied Air conditioning units for the Mercedes models, which are usually mid 1970s-1981ish are absolute crap….and ran on a zillion vacuum controlled operations…it’s a miracle if you find one that works even 50%….Mercedes introduced a new unit around 1982 that was also automatic and they are reliable but do a horrible job on the automatic part lol
A very interesting article, thank you! I have been the driver of several company BMW’s, the latest is a 318D (G20) – the ATC is terrible as it has been in all the others. It definitely doesn’t keep the temperature anywhere close to what it’s set to, if I set it to 21,5 C on a sunny day I’m quite warm and then when the sun goes down it’s immediately cold in the cabin – also on the same setting it will blow very chilly air and then warm while outside the temp is rock steady and not sunny. I usually end up cracking open a window because it’s such an unpleasant experience – I would much prefer just to be able to set a hot/cold dial. In my private Lexus it just works so probably a question of how the thing is set up.