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
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.
My new Subi needs a”Desert Mode”. It may be just fine up in Maine, Colorado or Washington, but in Texas it struggles to cool the 100 degree air. Usually comes out about 85 degrees with cabin recirculation off. I expect about 90 degree temp in the car this Summer. Hope the dealer finds something wrong with it and it gets fixed.
Turn cabin recirculation on….? It’s pretty tall order to ask an AC system to have a 50 degree temperature drop.
I do most of the time, but occasionally I need fresh air. Turning off recirculation or rolling down the windows is usually about the same result in interior temp. One is just faster than the other.
I’ve been told by mechanics that realistically I should expect a 20 degree cooling. More if the fan speed is lower, compressor speed is higher and with airflow over the condenser.
Drives around in Hell on Earth and complains about the heat. I suppose you also live adjacent to an international airport, a wastewater treatment plant, an elementary school with a huge playground, and an Amazon warehouse with 6,000 truck movements per day.
Between my job and my wife’s, we are sorta where we are for the next 10 years. Aside from the heat, we live in a nice area.
I gotta find something to complain about and the heat is an easy target.
And when it’s not hot, I suggest complaining about clouds.
And if there are no clouds, complain about there being no clouds!
You’ll have an endless complaining loop!
Thx for the ideas.
I lived in Austin for four years. Austin and the rest of the Hill Country is too humid to be considered a desert. Western Texas might be dry enough for AMC’s Desert mode to function without icing the condenser.
Weird… I have a 2015 Crosstrek in Georgia and it’s frigid in that thing in summer.
My new Subi needs a”Desert Mode”. It may be just fine up in Maine, Colorado or Washington, but in Texas it struggles to cool the 100 degree air. Usually comes out about 85 degrees with cabin recirculation off. I expect about 90 degree temp in the car this Summer. Hope the dealer finds something wrong with it and it gets fixed.
Turn cabin recirculation on….? It’s pretty tall order to ask an AC system to have a 50 degree temperature drop.
I do most of the time, but occasionally I need fresh air. Turning off recirculation or rolling down the windows is usually about the same result in interior temp. One is just faster than the other.
I’ve been told by mechanics that realistically I should expect a 20 degree cooling. More if the fan speed is lower, compressor speed is higher and with airflow over the condenser.
Drives around in Hell on Earth and complains about the heat. I suppose you also live adjacent to an international airport, a wastewater treatment plant, an elementary school with a huge playground, and an Amazon warehouse with 6,000 truck movements per day.
Between my job and my wife’s, we are sorta where we are for the next 10 years. Aside from the heat, we live in a nice area.
I gotta find something to complain about and the heat is an easy target.
And when it’s not hot, I suggest complaining about clouds.
And if there are no clouds, complain about there being no clouds!
You’ll have an endless complaining loop!
Thx for the ideas.
I lived in Austin for four years. Austin and the rest of the Hill Country is too humid to be considered a desert. Western Texas might be dry enough for AMC’s Desert mode to function without icing the condenser.
Weird… I have a 2015 Crosstrek in Georgia and it’s frigid in that thing in summer.
I wish BMW had desert-only modes, as my 2-series had a tendency to freeze over and lose A/C on trips across the Midwest while on automatic climate control settings. I think there may have been a software recall available, but I sold it before I got to check.
Apparently I am not the only one whos had this issue in a BMW
Yep, had the same happen in a friend’s F32 428i on a long trip several years ago. Baffling that a new, relatively expensive car would screw up something so basic as A/C.
I wouldn’t be surprised if they did all the thorough testing for temperature ranges across Europe and then just failed to consider humid climates.
I’m convinced in terms of air conditioning the Germans were putting one over on us in the ’70s. Mercedes or BMW a/c was about as powerful and cool as a baby’s breath. The aircooled Porsche 911 (maybe post 1989 are better) has the most indecipherable ventilation controls I’ve ever seen and when set properly with the blower on max, it sounds like a large wet/dry vac is in the cabin with you.
I wish BMW had desert-only modes, as my 2-series had a tendency to freeze over and lose A/C on trips across the Midwest while on automatic climate control settings. I think there may have been a software recall available, but I sold it before I got to check.
Apparently I am not the only one whos had this issue in a BMW
Yep, had the same happen in a friend’s F32 428i on a long trip several years ago. Baffling that a new, relatively expensive car would screw up something so basic as A/C.
I wouldn’t be surprised if they did all the thorough testing for temperature ranges across Europe and then just failed to consider humid climates.
I’m convinced in terms of air conditioning the Germans were putting one over on us in the ’70s. Mercedes or BMW a/c was about as powerful and cool as a baby’s breath. The aircooled Porsche 911 (maybe post 1989 are better) has the most indecipherable ventilation controls I’ve ever seen and when set properly with the blower on max, it sounds like a large wet/dry vac is in the cabin with you.
While it is no longer part of my work life, as I have changed engineering disciplines, I have had to explain how air conditioners work so many times it has become permanently etched into my mind. I read the lede, completely unaware that AMC included that setting but knowing full well why due to the aforementioned suffering of constantly telling people to stop being dumb and playing with the thermostats (in my case, at industrial facilities).
I’m about to rebuild the air conditioning system in my project vehicle and will be explaining the mechanics of the system to whichever of my kids I can coerce to help me. I’ll be replacing the condenser, compressor, evaporator, and orifice tube, and boy will my kids regret tacitly agreeing to the multi-hour explanation that comes with each component…
I had quite a few stumped when I tried to push for using exhaust stack heat to produce cooling for the plant, Absorbtion Chillers seem like a neat idea, but obviously the ammonia part scared them a bit.
My old pop-up camper has an absorption fridge using ammonia, uses either propane or a 120V heating element to heat the liquid. It still works!
Like an Icyball?
https://crosleyautoclub.com/IcyBall/crosley_icyball.html
I thought that something like this would be perfect for brewing beer, where you have to get a lot of liquid from boiling hot to almost freezing cold quickly. Homebrewing usually uses a lot of propane and water to heat and chill the beer.
I used to use an old dehumidifier with the case removed to explain the process to my students in the science lab. Just explain that where you want the heat, cold, and condensed moisture all depends on what appliance you are talking about.
A few years ago we had some flooding in my house after a historic level of rain swamped the area and my sump pump couldn’t keep up. I cleaned the carpets as much as I could and pulled out the industrial-sized dehumidifier (it was a lavish expense when I bought it but has paid for itself since) and let it do it’s thing. My wife asked why the house was getting so hot, and I was about two minutes into my explanation of how it functioned when she put her hand up and told me that much like when I tried to explain how the HVAC in the house works, she didn’t need to know the details of how it works, just that it does.
That is so funny. I get that. My wife does stuff like that to me also. great story.
I can’t believe “orifice tube” is an actual part. I’m content to forsake the explanation and just chortle.
There’s a ball cock in your toilet. Google that if you dare.
I used to supervise a bunch of industrial electricians and had fun constantly explaining to non-electrical folks that while my guys did use a lot of colorful language, not all of it was intended to be derogatory: https://nationaltradesman.com/2019/04/16/the-story-of-peckerhead/
I forget the theory often enough, but I’m vaguely aware that there are a whole bunch of practical details around AC maintenance and repair too. It’s a complicated topic.
Sounds like you’re well versed to handle your upcoming repair, I hope it goes well!
While it is no longer part of my work life, as I have changed engineering disciplines, I have had to explain how air conditioners work so many times it has become permanently etched into my mind. I read the lede, completely unaware that AMC included that setting but knowing full well why due to the aforementioned suffering of constantly telling people to stop being dumb and playing with the thermostats (in my case, at industrial facilities).
I’m about to rebuild the air conditioning system in my project vehicle and will be explaining the mechanics of the system to whichever of my kids I can coerce to help me. I’ll be replacing the condenser, compressor, evaporator, and orifice tube, and boy will my kids regret tacitly agreeing to the multi-hour explanation that comes with each component…
I had quite a few stumped when I tried to push for using exhaust stack heat to produce cooling for the plant, Absorbtion Chillers seem like a neat idea, but obviously the ammonia part scared them a bit.
My old pop-up camper has an absorption fridge using ammonia, uses either propane or a 120V heating element to heat the liquid. It still works!
Like an Icyball?
https://crosleyautoclub.com/IcyBall/crosley_icyball.html
I thought that something like this would be perfect for brewing beer, where you have to get a lot of liquid from boiling hot to almost freezing cold quickly. Homebrewing usually uses a lot of propane and water to heat and chill the beer.
I used to use an old dehumidifier with the case removed to explain the process to my students in the science lab. Just explain that where you want the heat, cold, and condensed moisture all depends on what appliance you are talking about.
A few years ago we had some flooding in my house after a historic level of rain swamped the area and my sump pump couldn’t keep up. I cleaned the carpets as much as I could and pulled out the industrial-sized dehumidifier (it was a lavish expense when I bought it but has paid for itself since) and let it do it’s thing. My wife asked why the house was getting so hot, and I was about two minutes into my explanation of how it functioned when she put her hand up and told me that much like when I tried to explain how the HVAC in the house works, she didn’t need to know the details of how it works, just that it does.
That is so funny. I get that. My wife does stuff like that to me also. great story.
I can’t believe “orifice tube” is an actual part. I’m content to forsake the explanation and just chortle.
There’s a ball cock in your toilet. Google that if you dare.
I used to supervise a bunch of industrial electricians and had fun constantly explaining to non-electrical folks that while my guys did use a lot of colorful language, not all of it was intended to be derogatory: https://nationaltradesman.com/2019/04/16/the-story-of-peckerhead/
I forget the theory often enough, but I’m vaguely aware that there are a whole bunch of practical details around AC maintenance and repair too. It’s a complicated topic.
Sounds like you’re well versed to handle your upcoming repair, I hope it goes well!
My grandfather bought a Mustang new in ’68, and had an aftermarket AC unit installed. My dad (8 at the time) thought that the AC was super cool (pun not inten…. hell, I’ll take credit for it) because it would get so cold it would blow snow. Sounds like it didn’t cycle the compressor, or at least not much, at the max setting.
My grandfather bought a Mustang new in ’68, and had an aftermarket AC unit installed. My dad (8 at the time) thought that the AC was super cool (pun not inten…. hell, I’ll take credit for it) because it would get so cold it would blow snow. Sounds like it didn’t cycle the compressor, or at least not much, at the max setting.
Rare Classic Cars and Automotive History is one of my favorite Youtube channels. It’s a must watch if you’re into 70’s and 80’s American cars.
This article is basically a summary of one of the recent videos from that channel.
Written credit should have been given to the Rare Classic Cars and Automotive History channel in the first paragraph. Seems to be a glaring oversight that really should be corrected. It’s more than a coincidence that this unique feature is covered here only days after the video was released.
Rare Classic Cars and Automotive History is one of my favorite Youtube channels. It’s a must watch if you’re into 70’s and 80’s American cars.
This article is basically a summary of one of the recent videos from that channel.
Written credit should have been given to the Rare Classic Cars and Automotive History channel in the first paragraph. Seems to be a glaring oversight that really should be corrected. It’s more than a coincidence that this unique feature is covered here only days after the video was released.
Honestly I didn’t expect this article to be as interesting as it was.
Thank you.
Honestly I didn’t expect this article to be as interesting as it was.
Thank you.
AMC really tried to push air conditioning, increasingly to distract customers from an aging lineup – for brief periods in the late ’70s/early ’80s, they’d run promotions offering “free” standard air conditioning on the Spirit and Concord to get customers in the door, since a/c was still kind of a big deal on small cars at the time. Though it didn’t move the sales figures much
They also kept on using the Weather Eye brand name on their climate control systems all the way through the 1978 Gremlin, even through the underlying engineering changed a lot from the old Nash-Kelvinator designs.
AMC really tried to push air conditioning, increasingly to distract customers from an aging lineup – for brief periods in the late ’70s/early ’80s, they’d run promotions offering “free” standard air conditioning on the Spirit and Concord to get customers in the door, since a/c was still kind of a big deal on small cars at the time. Though it didn’t move the sales figures much
They also kept on using the Weather Eye brand name on their climate control systems all the way through the 1978 Gremlin, even through the underlying engineering changed a lot from the old Nash-Kelvinator designs.
I also thank you for the article when I had a 73 Javelin a few years back I wondered about the desert only button never go to try it though as the A/C components had been removed from the car. But I am sure it had gotten some use back in the day as the Javelin came from Arizona if I am not mistaken (had to replaced the fuel filter on it as it was filled with sand).
I also thank you for the article when I had a 73 Javelin a few years back I wondered about the desert only button never go to try it though as the A/C components had been removed from the car. But I am sure it had gotten some use back in the day as the Javelin came from Arizona if I am not mistaken (had to replaced the fuel filter on it as it was filled with sand).
This is cool.
The door’s over there, Canopy.
This is cool.
The door’s over there, Canopy.
In my day-to-day life as a handyman for a homeless shelter, I am constantly correcting people who misuse the thermostats. Even the new units can and do freeze over, and then people complain that their AC isn’t working.
In steamy Tennessee, it’s an issue every single summer. I set limits on the thermostats to prevent users turning them too low, but they have internet access and look up the manuals to change the limits.
In my day-to-day life as a handyman for a homeless shelter, I am constantly correcting people who misuse the thermostats. Even the new units can and do freeze over, and then people complain that their AC isn’t working.
In steamy Tennessee, it’s an issue every single summer. I set limits on the thermostats to prevent users turning them too low, but they have internet access and look up the manuals to change the limits.
Thank you for this article! I’ve got a ‘74 Javelin with the factory AC. My wife and I always joke that we can’t use that setting because we live in Michigan.
Thank you for this article! I’ve got a ‘74 Javelin with the factory AC. My wife and I always joke that we can’t use that setting because we live in Michigan.
The “Dessert only” setting causes frosting with sprinkles to come out of the vents.
Mmm.. kind of like Dippin’ Dots! 😉
I prefer the Reddi-Wip dessert option myself. Just make sure a shower will be available at your destination.
AMC may have survived if they found a way to make their cars produce ice cream on demand.
The flavor should match the external color of the car.
AMC loved Brown.
Will pass as it wouldn’t likely be chocolate
The “Dessert only” setting causes frosting with sprinkles to come out of the vents.
Mmm.. kind of like Dippin’ Dots! 😉
I prefer the Reddi-Wip dessert option myself. Just make sure a shower will be available at your destination.
AMC may have survived if they found a way to make their cars produce ice cream on demand.
The flavor should match the external color of the car.
AMC loved Brown.
Will pass as it wouldn’t likely be chocolate