The vast majority of cars on the market have very similar controls. Indicator stalks, accelerator and brake pedals, and volume knobs all used to be fairly standard across the industry. What really lights up our dopamine receptors as enthusiasts are when we find something on a car we’ve never seen anywhere else. A great example comes to us from American Motors Corporation, who used to equip their cars with a special “Desert Only” setting.
If you’ve driven any modern off-roaders, you might be thinking this involved some kind of suspension tweak or differential lock. After all, everything from the Toyota RAV4 to the Porsche 911 Dakar has a “Sand” drive mode these days for tweaking traction control or other handling parameters.
In the case of vintage AMC products, though, it was unrelated to the vehicle’s driving performance entirely. Instead, it was all about the air con. No, I’m not kidding.
Only In The Desert, Promise
Just about every car comes with air conditioning these days, but it wasn’t always thus. Once upon a time, you were lucky enough to get some kind of ventilation system, or maybe a basic heater. By the early 1960s, around 20% of cars had air conditioning in the US.
By this point, Nash had set the standard that would become typical for automotive air-conditioning. The work started with the thermostatically-controlled “Weather Eye” heater from 1939. A bit over a decade later, the 1954 model year would see the introduction of the “All-Weather Eye” on the new Nash Ambassador, Statesman, and Rambler models. It combined air conditioning, heating, and ventilation into one combined unit. The system had a single control panel that brought all the controls together in one place on the dash, and the components of the system were all accessible under the hood. This was a big advance from earlier systems from other automakers, which often had separate air conditioning and heater systems entirely.
It was no coincidence that Nash made a big move here. The company had significant experience in vapor-compression refrigeration thanks to its merger with Kelvinator in 1937. The latter company is famous for fridges, which use effectively the same techniques for cooling as automotive air conditioners.
Also in 1954, Nash merged with Hudson to become the American Motors Corporation. Then the largest corporate merger in US history, it would see the new company eventually start releasing cars under the AMC name. It fought to maintain a position in the market against the brutal onslaught brought by the Big Three, innovating along the way. AMC would in fact become the first company to make air conditioning standard on an entire model line with the 1968 Ambassador. The underdogs at AMC even beat Lincoln and Cadillac to the punch with that move.
By the early 1970s, AMC began including the special Desert Only setting on its Weather Eye HVAC control panels. In this era, AMC had separate temperature controls for the air conditioning and heating. You could set the heater anywhere from OFF to the maximum WARM setting. As for the air conditioning, you’d use a slider or a knob to control temperature. At its lowest, the air conditioning compressor would be off. You could turn it colder, up until a certain point. Beyond that, the dial was marked DESERT ONLY. Basically, you could get the coldest possible temperature out of the air conditioning on this setting, but you were only supposed to use it in the desert.
To understand why, we need to understand the basics of vapor-compression refrigeration. It sounds complicated because it is, but I’ll give you a crash course based on AMC’s own technical manual from 1973. I’ll give you a full explanation in the next paragraph, but if that’s too much, breeze through and keep reading. I’ll provide a simpler one after that.
As per the diagrams above, the air conditioning unit consists of a closed loop full of refrigerant. In the case of AMC’s vintage designs, the systems used dichlorodifluoromethane, also known as R-12. In the loop, the compressor takes in refrigerant as a low-pressure gas and compresses it to a higher pressure. This causes it to heat up. It then passes to the condenser, which is essentially a big heat exchanger. The hot refrigerant gives up its heat to the atmosphere through the condenser, remaining at high pressure, but cooling to the point it becomes a liquid. From there, it passes to the expansion valve, where it goes from being a liquid under high pressure to a liquid at quite low pressure. This cools the refrigerant down significantly. It then passes through another heat exchanger, called the evaporator. Here, the cold liquid refrigerant sucks up heat from air passing over the evaporator. As the refrigerant sucks up heat from the air, it becomes a gas once more, while the air passing over the evaporator is cooled in turn. This generates the cold air flow desired from the air conditioner. Meanwhile, the gaseous refrigerant runs back to the compressor to be recompressed and reheated to continue the cycle.
If that’s too complex, all you need to know is this. In the air conditioner, the blower fan blows air over the evaporator to cool it down. This cold air is then sent out the vents to reduce the temperature in the cabin. The longer you run the compressor, the cooler the evaporator gets, and the colder the output from the air con. The temperature of the evaporator, and thus the output air, can be controlled by how long you run the compressor. If you leave it on all the time, it gets very cold. If you cycle it off and on to varying degrees, the evaporator, and thus the output, doesn’t get as cold.
Since the evaporator is cold, condensation tends to form on it during normal operation. The higher the humidity in the air, the more condensation forms. Similarly, the cooler the evaporator runs, the more condensation there is. At extremes, the condensation can even freeze onto the evaporator. This tends to block airflow through the evaporator, which cuts the flow of cold air to the cabin. The ice also tends to act as an insulating material, stopping the transfer of heat from the airflow to the refrigerant inside. Instead, the blower fan is just blowing over a big ice cube, which is not a very effective manner of cooling at all.
There’s one way around this, and it’s where the Desert Only mode comes in. We think of deserts as hot, and that’s often true. However, deserts are really defined by their lack of moisture. You can expect humidity to be very low in a desert climate. Thus, in such conditions, you can run the evaporator very cold with little to no risk of it freezing over. It’s not so much because the desert is hot, but because there’s little to no water in the air to freeze up the evaporator coils.
In Desert Only mode, the compressor is run continuously, making the evaporator very cold indeed. The air conditioner provides maximum cooling in this mode, but it will only work in dry conditions. If you try to use the Desert Only setting in more humid conditions, you’ll find the air conditioning loses its effectiveness in short order. Simply switching it back to a lower setting should allow it to recover in short order. Any ice buildup will clear quickly enough and the system can resume regular operation.
Why Don’t Cars Have Desert Only Settings Today?
There are a number of reasons behind that. For one thing, it’s generally poor practice to give the public buttons that mess things up if they’re used incorrectly. For example, if you set your AC to Desert Only mode in humid ol’ Florida, you’re probably going to wonder why it stops working all the time. Indeed, AMC’s own service manual instructed technicians to educate owners if they demanded a fix for their fully functional car after making this mistake.
There’s also something to be said about design choices. Many automakers simply didn’t feel the need to give customers air-conditioners that could go flat out and possibly freeze themselves over. Beyond that, technology has moved on. Modern computer-controlled air conditioners have temperature sensors on the evaporator coils that detect when they’re getting too cold. When this happens, the compressor can be shut off to let the evaporator warm back up to a temperature above freezing.
Indeed, AMC itself would abandon the Desert Only setting after just a few years. By the mid-1970s, it had started manufacturing HVAC controls with a single combined slider that went from cold to warm, as is familiar to us today. No more could you wind the coldness out to 11 and put your evaporator at risk of freezing over. More’s the pity.
Don’t worry if you’ve forgotten how air conditioners work by the time you’ve finished this article. I forget all the time and I took Heat Transfer & Thermodynamics in University (good course, by the by). What you do know, however, is how and why AMC built cars with a weird Desert Only setting in the early 1970s. That should give you plenty to bloviate about at your next classic car meet when you get sick of the endless blather about hemispherical combustion chambers from the Mopar set. It’s good to mix it up a little, you know?
Image credits: Nash, AMC, Hemmings, via eBay
Top graphic images: Hemmings
And even more commonly known as “freon”.
It is, but several other refrigerants, including r134a, are also commonly known as Freon.
And even more commonly known as “freon”.
It is, but several other refrigerants, including r134a, are also commonly known as Freon.
This was an issue with 1st Gen Honda Fits as well. High humidity would freeze up the coils,more so if you had it on recirc, but would occur on both regardless. It became a bit of a game for me on long trips on adjusting temp and direction of airflow to try and prevent as no dealership could ever get it to reproduce the issue. C/Ds long term tester also had the issue in their write-up
This was an issue with 1st Gen Honda Fits as well. High humidity would freeze up the coils,more so if you had it on recirc, but would occur on both regardless. It became a bit of a game for me on long trips on adjusting temp and direction of airflow to try and prevent as no dealership could ever get it to reproduce the issue. C/Ds long term tester also had the issue in their write-up
Umm, is it for when you need to ditch the car in a hurry?
Umm, is it for when you need to ditch the car in a hurry?
Can we all pause to notice Nash gave you an honest to god cabin filter in 1954? I thought the ad copy of “Fresh filtered air” was bluster.
Nash was legitimately ahead of their time in a lot of ways
Can we all pause to notice Nash gave you an honest to god cabin filter in 1954? I thought the ad copy of “Fresh filtered air” was bluster.
Nash was legitimately ahead of their time in a lot of ways
Oh, I can tell you that mid-2010s Mercedes Sprinters have this mode; they just can’t be bothered to mark it as such.
I rented a Sprinter crew van in 2017 to drive to the Oregon Eclipse festival. It’s was a hot day in California’s Central Valley, and the air conditioner seemed to fail. This was going to be a long ride to Oregon.
I noticed that, after stopping for a bite to eat, that the cold air came back for a while, before going away again. At this point I recalled that *something* in an AC unit could freeze over, and reasoned that if I turned it off for a bit, it might resolve the issue. It worked so well that apparently due to how the system was packaged, it actually threw droplets of water out the vents. Success! My friends were duly impressed as they were not the sort to folks who were experienced with the scientific method and troubleshooting machines.
Eventually I tuned in a setting for the HVAC that was a bit warmer than I’d otherwise prefer, but nonetheless didn’t ice over, so it could stay on. So the moral of the story is that Mercedes does make a desert-only mode for their AC, they just don’t bother to mark where that mode is on their controls.
Oh, I can tell you that mid-2010s Mercedes Sprinters have this mode; they just can’t be bothered to mark it as such.
I rented a Sprinter crew van in 2017 to drive to the Oregon Eclipse festival. It’s was a hot day in California’s Central Valley, and the air conditioner seemed to fail. This was going to be a long ride to Oregon.
I noticed that, after stopping for a bite to eat, that the cold air came back for a while, before going away again. At this point I recalled that *something* in an AC unit could freeze over, and reasoned that if I turned it off for a bit, it might resolve the issue. It worked so well that apparently due to how the system was packaged, it actually threw droplets of water out the vents. Success! My friends were duly impressed as they were not the sort to folks who were experienced with the scientific method and troubleshooting machines.
Eventually I tuned in a setting for the HVAC that was a bit warmer than I’d otherwise prefer, but nonetheless didn’t ice over, so it could stay on. So the moral of the story is that Mercedes does make a desert-only mode for their AC, they just don’t bother to mark where that mode is on their controls.
Kick ass on referencing Rare & Classic Cars channel! I watch it all the time, and you posted his most recent video on desert mode… and maybe it was this story inspiration. He covers all the weird bonkers design decisions over time from US manufacturers.
Kick ass on referencing Rare & Classic Cars channel! I watch it all the time, and you posted his most recent video on desert mode… and maybe it was this story inspiration. He covers all the weird bonkers design decisions over time from US manufacturers.
Man, love this site! Have been an AMC fan for a while, but never knew about this, and wonderfully explained. Torch, can you do an article on the HVAC of aircooled 911s? It’s impressively complex/not intuitive; I have owned mine 10 years and don’t really understand what any of the levers actually do apart from the red ones next to the seats
https://i.imgur.com/XV7HUCB.jpeg
Man, love this site! Have been an AMC fan for a while, but never knew about this, and wonderfully explained. Torch, can you do an article on the HVAC of aircooled 911s? It’s impressively complex/not intuitive; I have owned mine 10 years and don’t really understand what any of the levers actually do apart from the red ones next to the seats
https://i.imgur.com/XV7HUCB.jpeg
“For one thing, it’s generally poor practice to give the public buttons that mess things up if they’re used incorrectly”
Traditionally in automobiles those functions are reserved fir the pedals and the steering wheel.
“For one thing, it’s generally poor practice to give the public buttons that mess things up if they’re used incorrectly”
Traditionally in automobiles those functions are reserved fir the pedals and the steering wheel.
European automakers should tear apart one of these old AMCs to figure out how A/C works.
Many Japanese automakers too. The AC on my CX-50 really struggles to cool the car down on a hot day; if you get stuck in traffic you’re gonna get hot. Even while moving, if it’s over like 85ish, the system just keeps fan blasting full speed with only somewhat cool air coming out. My 3rd gen Tacoma, while better, wasn’t all that much better. Pretty much any American car can make your car straight up refrigerator-like in near any environment. It’s crazy how much better A/C works in American cars.
Same with my Subaru. Oh boy, and if you want a bit of passing power while the AC is on, you won’t get it and the AC will noticeably weaken.
The Hondas we’ve owned haven’t had bad AC systems (when they aren’t failing), but they weren’t going to win any contests.
Recently bought a 2016 Toyota Camry and that thing will keep your beer cold just sitting in a parking lot.
If there was anything about 1980s GM cars that I liked, it was their AC systems. The engines might overheat sitting in traffic, but until that happened, you stayed cool.
My kid’s ’92 Camry has been converted to R134 and it’s POLAR. I’m talkin’ Kelvin here.
I’m guessing there is more nuance here. Crossovers in general might be more likely to struggle because they may be repurposing HVAC components from hatchback platforms for a larger cabin volume.
Nissans in general and Altimas in particular are incredibly popular in the Deep South. I think not coincidentally, the A/C in them pumps.
And then there’s my Miata. It has a smaller cabin than the hatchbacks its HVAC system comes from, and it will happily roast or freeze you. But the A/C also saps so much power that there’s switch in the throttle pedal that turns off the A/C when you’re at more than 3/4 throttle, which is both brilliant and silly.
I came from a Subaru SVX which had an AC system that could put up a good fight against GM’s finest to an RX8 I pre-ordered and thought the AC was particularly wimpy. As this was a very early car I talked to the dealer about it and they did a factory authorized modification to keep the compressor engaged longer. It definitely made an improvement, however it also came with the side effect of the evaporator freezing over when super humid, aka SC, GA, and FL. For every 30 minutes of AC on I’d need to turn it off for 5 minutes and you’d sometimes see small bits of ice shooting out of the vents as it thaws.
I owned an SVX for 7 years; and I have an AC story for you: My SVX was black with the charcoal interior. It was a 90 degree day, high humidity, and I had a 1.5 hour drive to Milwaukee. Half way there, the AC quit working. Within a short time, the copious amount of glass on SVX, with those tiny little side windows, became a pressure cooker. Didn’t matter if all 4 tiny windows and the sunroof were open, I was dripping. So I put on cruise control and started stripping.
When I got to MKE, I was only in my underwear, hoping nobody would notice.
In Milwaukee, no one would notice.
Yeah, AC in my 2013 4Runner sucks. I bought it in 2019, the following summer I had to have it recharged because it barely worked. That lasted a few years, now it’s back to not blowing cold air. I’m assuming now that it has a small leak somewhere, if I can get 3 seasons out of a recharge, I’ll just keep doing that rather than spend the money to actually fix it. I watched a Car Care Nut video about Toyota AC, I cannot imagine the cost of the labor charge for that level of disassembly. They completely stripped out the dash right down to the firewall. I’m now wondering if the AC issue was why the PO traded it with 79K miles. That doesn’t seem typical for a 4R owner.
Buy a Toyota they said, it’ll be reliable they said.
I don’t understand people who turn the fan speed up when they want max cooling. If your compressor is maxed out, having the fan lower will keep the car cooler, because there’s less warm air being pumped through the cooling bit.
Sounds like you don’t understand thermodynamics, but ok.
My Volvo 740s A/C could cool only my crotch
Depending on the size of your crotch, this could be very impressive, or very disappointing.
Euro cars used to have so-so ACs, but that was back in the 80’s. Even my wife’s 9 year old Fiat 500 has a very frigid AC.
My 2012 XC70 has A/C that works great down in Southern Arizona! I only go through two A/C compressor clutches every five years!
European automakers should tear apart one of these old AMCs to figure out how A/C works.
Many Japanese automakers too. The AC on my CX-50 really struggles to cool the car down on a hot day; if you get stuck in traffic you’re gonna get hot. Even while moving, if it’s over like 85ish, the system just keeps fan blasting full speed with only somewhat cool air coming out. My 3rd gen Tacoma, while better, wasn’t all that much better. Pretty much any American car can make your car straight up refrigerator-like in near any environment. It’s crazy how much better A/C works in American cars.
Same with my Subaru. Oh boy, and if you want a bit of passing power while the AC is on, you won’t get it and the AC will noticeably weaken.
The Hondas we’ve owned haven’t had bad AC systems (when they aren’t failing), but they weren’t going to win any contests.
Recently bought a 2016 Toyota Camry and that thing will keep your beer cold just sitting in a parking lot.
If there was anything about 1980s GM cars that I liked, it was their AC systems. The engines might overheat sitting in traffic, but until that happened, you stayed cool.
My kid’s ’92 Camry has been converted to R134 and it’s POLAR. I’m talkin’ Kelvin here.
I’m guessing there is more nuance here. Crossovers in general might be more likely to struggle because they may be repurposing HVAC components from hatchback platforms for a larger cabin volume.
Nissans in general and Altimas in particular are incredibly popular in the Deep South. I think not coincidentally, the A/C in them pumps.
And then there’s my Miata. It has a smaller cabin than the hatchbacks its HVAC system comes from, and it will happily roast or freeze you. But the A/C also saps so much power that there’s switch in the throttle pedal that turns off the A/C when you’re at more than 3/4 throttle, which is both brilliant and silly.
I came from a Subaru SVX which had an AC system that could put up a good fight against GM’s finest to an RX8 I pre-ordered and thought the AC was particularly wimpy. As this was a very early car I talked to the dealer about it and they did a factory authorized modification to keep the compressor engaged longer. It definitely made an improvement, however it also came with the side effect of the evaporator freezing over when super humid, aka SC, GA, and FL. For every 30 minutes of AC on I’d need to turn it off for 5 minutes and you’d sometimes see small bits of ice shooting out of the vents as it thaws.
I owned an SVX for 7 years; and I have an AC story for you: My SVX was black with the charcoal interior. It was a 90 degree day, high humidity, and I had a 1.5 hour drive to Milwaukee. Half way there, the AC quit working. Within a short time, the copious amount of glass on SVX, with those tiny little side windows, became a pressure cooker. Didn’t matter if all 4 tiny windows and the sunroof were open, I was dripping. So I put on cruise control and started stripping.
When I got to MKE, I was only in my underwear, hoping nobody would notice.
In Milwaukee, no one would notice.
Yeah, AC in my 2013 4Runner sucks. I bought it in 2019, the following summer I had to have it recharged because it barely worked. That lasted a few years, now it’s back to not blowing cold air. I’m assuming now that it has a small leak somewhere, if I can get 3 seasons out of a recharge, I’ll just keep doing that rather than spend the money to actually fix it. I watched a Car Care Nut video about Toyota AC, I cannot imagine the cost of the labor charge for that level of disassembly. They completely stripped out the dash right down to the firewall. I’m now wondering if the AC issue was why the PO traded it with 79K miles. That doesn’t seem typical for a 4R owner.
Buy a Toyota they said, it’ll be reliable they said.
I don’t understand people who turn the fan speed up when they want max cooling. If your compressor is maxed out, having the fan lower will keep the car cooler, because there’s less warm air being pumped through the cooling bit.
Sounds like you don’t understand thermodynamics, but ok.
My Volvo 740s A/C could cool only my crotch
Depending on the size of your crotch, this could be very impressive, or very disappointing.
Euro cars used to have so-so ACs, but that was back in the 80’s. Even my wife’s 9 year old Fiat 500 has a very frigid AC.
My 2012 XC70 has A/C that works great down in Southern Arizona! I only go through two A/C compressor clutches every five years!
I had a 98 Taurus that was originally an Arizona car; I lived in northern Ohio. It had a factory-installed heater bypass to keep hot coolant out of the passenger compartment. The A/C worked great. The heater and defroster had a difficult time keeping up during the cold Midwest winters, until I removed the bypass hose.
I had a 98 Taurus that was originally an Arizona car; I lived in northern Ohio. It had a factory-installed heater bypass to keep hot coolant out of the passenger compartment. The A/C worked great. The heater and defroster had a difficult time keeping up during the cold Midwest winters, until I removed the bypass hose.
Figured it had something to do with the humidity.
I’m not sure if I froze it up, or if it shut off to protect itself but driving my 2013 320i through Texas one summer I lost the AC for a bit after running it as cold as it would go for a couple hours. Took about 30 min to come back.
My first day in Texas (summer) freaked me the you-know-what out when heavy mist started pouring out of my vents.
Figured it had something to do with the humidity.
I’m not sure if I froze it up, or if it shut off to protect itself but driving my 2013 320i through Texas one summer I lost the AC for a bit after running it as cold as it would go for a couple hours. Took about 30 min to come back.
My first day in Texas (summer) freaked me the you-know-what out when heavy mist started pouring out of my vents.
Knowing old cars and old jeeps, for a moment I thought the desert mode was a heater setting to keep the car from overheating in the desert until I saw the article.
thats the secret desert only mode
Knowing old cars and old jeeps, for a moment I thought the desert mode was a heater setting to keep the car from overheating in the desert until I saw the article.
thats the secret desert only mode
R12 was great for refrigeration. Not so much for the environment. My father has an entire case of the stuff hidden from the EPA agents that are no doubt looking for him, or so he says.
Having a case of R-12 all sealed up in cans is not a bad thing. Releasing R-12 into the atmosphere, well, that’s a different story.
Is that a black helicopter I hear?
Old R12 is grandfathered in. It’s perfectly legal to own, buy, and sell any R12 made prior to the ban. It is not legal to import or make new R12.
The specific problem with R12 (and other chlorofluorocarbons) is that it degrades the ozone layer in the earth’s atmosphere. This lead to a hole in the ozone layer at the earth’s poles. The restrictions on chlorofluorocarbons from the mid-1990’s on are an example of a clear-cut success. The hole in the ozone layer is no more!
BTW – We are currently in the middle of a phase-down in the manufacturing and use of hydrofluorocarbon materials such as R134a. The problem with these hydrofluorocarbon materials (which in the case of R134a was the replacement for R12) is that they have very high Global Warming Potential. The GWP of R134a refrigerant is 1430 x higher than CO2! This phase-down has driven the auto industry toward low-GWP refrigerants. Most new cars today use HFO-1234YF refrigerant, which has a GWP of 4.