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View Full Version : Who decided how car heaters distribute hot air?


Heracles
01-30-2011, 09:39 AM
It's about heaters in cars. It's been bugging me for decades.

I have this general opinion that the people who design the winter-driving features for cars have never actually lived in cold weather.

In the 1970s, most cars had a slider that allowed you to decide if you wanted the hot air to be directed to your feet, to the windows for defrosting, or to the outlets in the dashboard that give warm air to your hands and face. The slider physically activated doors and valves in the air ducts, so you could have a mix of feet-and-windows or feet-and-head, but never windows-and-head. My dad's 1977 Dodge Monaco worked like this, and so did my 2002 Subaru Impreza.

Nowadays, most cars have electrically-activated valves in the air ducts, and have actual buttons you can push for the various combinations. But they've kept the old convention of not allowing you to defrost the windows and heat your hands-and-face at the same time. At least this is how my 2009 Honda Civic works, and all other cars that I know of.

My dad only wore thin winter soles on his leather shoes and wore rabbit-lined kid gloves, so I guess he needed the warm air mostly on his feet. My boots are plenty warm, but my gloves are not that good (and I keep forgetting them everywhere). So I need to defrost my windows and heat my hands, and my car won't allow it.

Why can't I use my heater as I see fit? How can I get the industry to change its evil ways?

Dead Cat
01-30-2011, 09:44 AM
I don't know the answer to your question, but the electronic climate control on my 2003 Peugeot (a French marque not sold in the US, I believe) allows any combination you want.

LSLGuy
01-30-2011, 10:15 AM
Yeah, the old slider wasn't real flexible. But ...

I've never seen a car with electronic controls that didn't permit all possible combinations of top, middle, & bottom.

Given that it snows in Detroit, all of Germany, and most of Japan, I rather doubt the folks who design these things are unaquainted with snow & cold.

Since the Civic is Honda's cheapest model, perhaps the problem is that cheapo cars cut corners where they can, and including a less-fancy heater gives them some whiz bang "enhancements" to crow about as you move up their model line.

Heracles
01-30-2011, 10:37 AM
I've never seen a car with electronic controls that didn't permit all possible combinations of top, middle, & bottom.

(...)

Since the Civic is Honda's cheapest model, perhaps the problem is that cheapo cars cut corners where they can, and including a less-fancy heater gives them some whiz bang "enhancements" to crow about as you move up their model line.

(Actually, in Canada at least, the Fit is the cheapest Honda, by a few hundred bucks.)

My Civic is a hydrid, with the pollen filter, thermostatic control, etc. The air flow is selected by pressing a MODE button that draws a little diagram on the display. And the MODE never reaches windows-and-head. I admit that the valves and deflectors underneath may be the same as for the cheaper Civics.

But I just looked up the manuals for the Lexus RX350 and LS460, and the Cadillac CTS. They all have the same limitation.

Heracles
01-30-2011, 11:49 AM
I don't know the answer to your question, but the electronic climate control on my 2003 Peugeot (a French marque not sold in the US, I believe) allows any combination you want.

Are you sure? You didn't specify which model you have, but I just looked up the Guides d'utilisation for the Peugeot 207 and 607, and found the same limitations.

(Along with literary gems such as salissures persistantes for hard-to-remove stains.)

Harmonious Discord
01-30-2011, 12:07 PM
Ma's car has no floor vent on the passenger side. Who ever designed it should be left to freeze to death in a Wisconsin snow bank. The passenger only gets heat from vents chest high in the dash.

california jobcase
01-30-2011, 12:15 PM
I had plenty of cars that had only floor and window vents. Two of them were old VWs, which means neither floor nor defrost worked worth a hoot.

Kevbo
01-30-2011, 12:36 PM
My 97 Ford truck is as the OP discribes. Not only that, if you have it on either of the two the defrost settings (windshield, windshield+feet) it cycles the AC compressor to dry the air...virtually never needed in this climate, and being that it is a diesel, I could really do without that cooling for the first 10 miles. Basically they kept the look and feel of the old slider/cable control but it is now electrical switches that control vacuum operated shutters.

DrCube
01-30-2011, 01:28 PM
Here's a heater question: Why isn't there an electric heater that can be used for the few minutes until the engine heats up? Sometimes people don't have time to start their car and let it heat up for awhile before going somewhere. Seems like a simple, cheap and useful feature. Is it just that it draws too much power?

Cleophus
01-30-2011, 01:46 PM
Seems like a simple, cheap and useful feature. Is it just that it draws too much power?

Yes. Let's say you wanted to base it on something like this small 900/1500 watt heater (http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&productId=100685920&langId=-1&catalogId=10053&ci_src=14110944&ci_sku=100685920&cm_mmc=shopping-_-googlebase-_-D27X-_-100685920&locStoreNum=1273). It would require up to 125 A of continuous current for 12 V operation.

Musicat
01-30-2011, 01:50 PM
Here's a heater question: Why isn't there an electric heater that can be used for the few minutes until the engine heats up? Sometimes people don't have time to start their car and let it heat up for awhile before going somewhere. Seems like a simple, cheap and useful feature. Is it just that it draws too much power?
The old VWs had a gasoline-powered, optional auxiliary heater for extreme climates. Never saw one anywhere else, tho.

Heracles
01-30-2011, 01:59 PM
Here's a heater question: Why isn't there an electric heater that can be used for the few minutes until the engine heats up? Sometimes people don't have time to start their car and let it heat up for awhile before going somewhere. Seems like a simple, cheap and useful feature. Is it just that it draws too much power?

I remember we used to have an electric area heater designed for car interiors, that you'd plug into the house AC outlet. Haven't seen a trace of those for years, though; probably a fire hazard (or worse, a lawsuit hazard).

In light airplanes, the heater usually draws heat not from a radiator, from the outside surface of the exhaust pipe (which is normally ahead of the cabin).

RealityChuck
01-30-2011, 02:15 PM
Our 1993 Saturn has a setting exactly as you describe. You've just been looking at the wrong cars.

Actually, though, I never use it.

california jobcase
01-30-2011, 02:43 PM
12V electric heaters are available at the large truck stops. Flying J, Pilot, and Travel America likely have them.

IvoryTowerDenizen
01-30-2011, 03:45 PM
Same complaint of my 2004 Honda Pilot. I cannot get defrost and face/hand warm setting. I can do face/hand alone, foot and face/hand, foot alone, defrost alone or defrost and foot.

Sigh.

Manda JO
01-30-2011, 03:55 PM
My 2008 Mazda does allow this combination--which I saw as a feature, as I'd noticed the same problem in my earlier cars. Furthermore, I still have sliders. I don't even have electric locks, let alone electric climate control.

Dead Cat
01-30-2011, 05:21 PM
Are you sure? You didn't specify which model you have, but I just looked up the Guides d'utilisation for the Peugeot 207 and 607, and found the same limitations.

(Along with literary gems such as salissures persistantes for hard-to-remove stains.)

It's a 206, and I'm pretty sure. If I remember, I will try to check in the next few days. It sticks in my head because there is only a single button to control this setting, and you have to press it several times to cycle through all the possible (six or seven) options.

Balthisar
01-30-2011, 05:30 PM
My 2001 Continental doesn't allow any combination of air direction. If I want defrost, I get defrost, or defrost+floor. Defrost heats my upper body quite well. "Auto" mode (it's climate control) directs heat only to the floor, but I can override that and direct heat to the floor+midlevel, or as said before, midlevel+defost. I almost never use midlevel; it's just not comfortable for heat. In AC mode, "Auto" directs to midlevel, and I agree with the car that that's the most comfortable.

I'm not sure what my 2004 Expedition does. I don't drive it enough. Even though it's never, it only has manual HVAC controls. I suspect that where I can direct the air is similar to my Lincoln. I think the Lincoln has separate driver/passenger controls, too (the Ford definitely doesn't).

New cars are actually much more flexible than older cars in this respect. They have either vacuum- or electrically-activated flapper doors that can direct the air anywhere, in theory. The old cars with the sliders mechanically linked a single flapper that allowed you gradually direct the air from floor to mid-level to defrost. I'm pretty sure you couldn't do it the "comfortable" way and have floor and defrost without mid-level.

bump
01-30-2011, 05:47 PM
I bet there's only a certain amount of air flow in CFM that comes out of the blower up under hte dash, and if they blew it out of the main registers and the defroster, you probably wouldn't get enough airflow to actually defrost.

My Dodge truck has a knob- it goes from full-on defrost, to defrost/feet, to feet/upper, to full upper, then to recirc upper, and recirc upper/feet (with intermediate gradations between each setting listed above.)

You use it in conjunction with the hot/cold knob and the A/C button to regulate the temp. It's essentially the old slider system in knob form, from what I can tell.

pullin
01-31-2011, 12:42 PM
In light airplanes, the heater usually draws heat not from a radiator, from the outside surface of the exhaust pipe (which is normally ahead of the cabin).

The twin-engined planes in our flight school have a little furnace in the nose that burns Avgas from the wing tanks. That's right... it squirts high octane gasoline into a little chamber and sets it on fire. What could possibly go wrong?

In answer to the OP, I think my 2010 Corolla actually has a choice where it blows on the windsheild and the mid-level vents. I'll try to remember and check this evening on my way home.

Tastes of Chocolate
01-31-2011, 12:47 PM
My 97 Ford truck is as the OP discribes. Not only that, if you have it on either of the two the defrost settings (windshield, windshield+feet) it cycles the AC compressor to dry the air...virtually never needed in this climate, and being that it is a diesel, I could really do without that cooling for the first 10 miles.

I hate this "feature" also. Really, if my windshield is fogged up, I'm smart enough to turn on the AC to clear it: don't make it mandatory. Give me the option of running the top level vents without the AC, dang it!

Johnny L.A.
01-31-2011, 09:30 PM
2005 Prius: Windshield defrost, Upper body, Feet, Upper body and feet, Windshield and feet.

I just wish I could figure out how to use the blower without having the a/c on. You know, just have the fan circulate the fresh air without doing anything to it (and using energy).

drachillix
01-31-2011, 10:22 PM
Same complaint of my 2004 Honda Pilot. I cannot get defrost and face/hand warm setting. I can do face/hand alone, foot and face/hand, foot alone, defrost alone or defrost and foot.

Sigh.

2006 Ridgeline RTS same here

3waygeek
02-01-2011, 10:19 AM
Here's a heater question: Why isn't there an electric heater that can be used for the few minutes until the engine heats up? Sometimes people don't have time to start their car and let it heat up for awhile before going somewhere. Seems like a simple, cheap and useful feature. Is it just that it draws too much power?

The old VWs had a gasoline-powered, optional auxiliary heater for extreme climates. Never saw one anywhere else, tho.Current VW & Audi TDIs have an auxiliary electric heater -- at least my A3 does. On cold mornings, I'll get warm air coming out of the ducts before the temperature gauge has even considered moving.

Johnny L.A.
02-01-2011, 11:10 AM
The old VWs had a gasoline-powered, optional auxiliary heater for extreme climates. Never saw one anywhere else, tho.

My '46 Willys CJ2A had one. I never used it. I gather gasoline-fueled heaters were fairly common in the first half of the last century.

Minnie Luna
02-01-2011, 11:11 AM
My 08 S4 has the windshield defrost setting separate from the cabin heater controls. It has the winter package, so I am not sure if this was standard on the S4 or if it is specific to the winter pack.

bouv
02-01-2011, 01:06 PM
Yes. Let's say you wanted to base it on something like this small 900/1500 watt heater (http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&productId=100685920&langId=-1&catalogId=10053&ci_src=14110944&ci_sku=100685920&cm_mmc=shopping-_-googlebase-_-D27X-_-100685920&locStoreNum=1273). It would require up to 125 A of continuous current for 12 V operation.

But plenty of cars have heated seat warmers, and those get plenty toasty. How many watts are those? Yes, it would be more taxing on the alternator which would then require more RPM's than the engine, but I think it would just be comparable to AC use in the summer.

stpauler
02-01-2011, 01:17 PM
2005 Prius: Windshield defrost, Upper body, Feet, Upper body and feet, Windshield and feet.

I just wish I could figure out how to use the blower without having the a/c on. You know, just have the fan circulate the fresh air without doing anything to it (and using energy).

I've got an 08 Prius and can just turn the A/C on/off with touching the A/C button and it keeps the fans blowing. It's got the recycled/fresh air button too. Looks just like this. (http://images.thecarconnection.com/med/2008-toyota-prius-5dr-hb-touring-natl-temperature-controls_100272354_m.jpg) (If you click on the speed, it will take it out of the AUTO mode).

Cleophus
02-01-2011, 01:46 PM
But plenty of cars have heated seat warmers, and those get plenty toasty. How many watts are those? Yes, it would be more taxing on the alternator which would then require more RPM's than the engine, but I think it would just be comparable to AC use in the summer.

A seat warmer requires considerably less power because it is warming a static material. A blower heater must become considerably hotter to transfer heat effectively to the cool air being continually sucked through it. The fuse for heated seats in my car, for example, is 15A for both seats. A regular electric blanket, which is larger than a car seat, might draw between 200 and 300 W, which corresponds to max of 25 A if it were powered by the car. The power equation for DC loads and AC resistive loads is P = V*I, where the power is equal to the voltage multiplied by the current. So, for a given power output, the current required increases as the voltage decreases. Since standard house line voltage is coincidentally 10 times more than a car's system, any heating device will require about 10 times more current in a car than a house to put out the same amount of heat energy.

Hampshire
02-01-2011, 02:35 PM
It's the way the ducts and valves are aligned. Since you have 3 options (face,feet,glass) no matter how you align the 3 the two on the ends can't be used together. Most are aligned FACE-FACE-FEET-FEET-GLASS-GLASS and the duct is two wide so the valve slides left to right giving you the options:
FACE-FACE-FEET-FEET-GLASS-GLASS
FACE-FACE-FEET-FEET-GLASS-GLASS
FACE-FACE-FEET-FEET-GLASS-GLASS
FACE-FACE-FEET-FEET-GLASS-GLASS
FACE-FACE-FEET-FEET-GLASS-GLASS

I suppose they could alter the order of the 3 but you'd lose one of the exsisting combos. Pretty sure they went with the most popular/funtional combos.

Johnny L.A.
02-01-2011, 02:40 PM
I've got an 08 Prius and can just turn the A/C on/off with touching the A/C button and it keeps the fans blowing. It's got the recycled/fresh air button too. Looks just like this. (http://images.thecarconnection.com/med/2008-toyota-prius-5dr-hb-touring-natl-temperature-controls_100272354_m.jpg) (If you click on the speed, it will take it out of the AUTO mode).

I've assumed that AUTO means that it will seek to maintain the desired temperature.

Dead Cat
02-02-2011, 04:39 PM
It's a 206, and I'm pretty sure. If I remember, I will try to check in the next few days. It sticks in my head because there is only a single button to control this setting, and you have to press it several times to cycle through all the possible (six or seven) options.Well, turns out I had misremembered - in fact there are only five options, and as the OP says, face and glass simultaneously is not one of them. Unlike the OP, however, I have never felt the lack. When it is set to "glass only", a small but significant amount of heat still comes out of the fascia vents.

I think Hampshire has hit the nail on the head with the explanation, well done! Of course, it does not have to be done that way, but it must be a lot cheaper than a fully electronic system that would allow all options.

curious11
02-03-2011, 12:03 PM
The 2002 Chevy Malibu allows...
Face, Face - Feet, Feet, Feet - Glass, Glass, so it Fits Hampshires Theory.

I dislike warm air blown in my face, so it never bothered me.

I did once read about a person who covered half his radiator with paper or cardboard to allow less cooling in very cold weather to have more heat come into the passanger compartment. You may have seen big trucks with canvas over their radiators, same idea.

kushiel
02-04-2011, 12:56 PM
On a related note, why won't my car run the rear defrost as soon as I turn the car on? I have a remote car starter, so I'll leave the defrost cranked up and turn the car on to warm up, but rear defrost requires you to press a button inside the vehicle to activate it, so I end up with every window defrosted except the rear which is still covered in frost. Is it because I have those strips that get heated themselves running on the window instead of vents?

Cisco
02-04-2011, 01:31 PM
Our 1993 Saturn has a setting exactly as you describe. You've just been looking at the wrong cars.

Actually, though, I never use it.

Can you show us a picture of that? My 1996 Saturn didn't have it. Seems weird that they would remove a feature like that on a later model.

Hampshire
02-04-2011, 01:58 PM
Is it because I have those strips that get heated themselves running on the window instead of vents?

I believe so. I think those are run on a timer or at least turn themselves off when you power off the car. I've heard if left on for too long they can overheat and damage themselves.

Si Amigo
02-04-2011, 03:02 PM
Who decided how car heaters distribute hot air?

It's about heaters in cars. It's been bugging me for decades.

I have this general opinion that the people who design the winter-driving features for cars have never actually lived in cold weather.

The federal government sets the standards (http://www.nhtsa.gov/cars/rules/import/fmvss/index.html#SN103) as to how you car is designed to operate; section 103 deals with heating and defrosting. Sorry, but I don't have time to get you a detailsed link to this section right now (time to go do some Friday night drinking! :) Individual car companies interpret the government standards differently and getting sued by someone (or many people) is what drives them to refine their interpretation; thus they all do it a little bit differently.