Sorry - but in this case it does. You have a nominal 12V that is literally divided across the resistor and the coil primary. In effect it is a voltage divider. You would analyze it for current and voltage nodes just like a voltage divider (current gets dropped over the "top" resistor, and the remainder is left for the "bottom" element). There are some a.c. interactions, but the effect is the same - i.e., the available voltage being shared across two elements suspended between a d.c. voltage and ground.
Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")
The reality is that there are common temperature situations in which the windshield fogs up making driving dangerous without the a.c. working, but does not without the a.c. working. That is a fact.
Absolutely. I never disuputed that.
I think you have made it *an* issue - it wasn't the original one.
Again, there are many real winter conditions where having the a.c. operating for defrost means the difference between a heavily fogged over windshield and a relatively clear one that is safe for driving.
I think Matt mis-stated reality there. That doesn't make Matt an evil person - that's all that needs to be said. I'm not here to agree altogether with one person and disagree with the other. I'm trying to state reality, and let the chips fall where they may.
I already checked and wasn't surprised to find no mention of it. But, as already stated, that's because it is a moot point this day and time with it being automatically taken care of with no operator interaction. I did expect to find a discussion on the FSM about automatic a.c. operation during defrost mode, but could find none.
You can argue the theory all you want. Again, fact is that with a.c. involvement, the windshield will not fog up in situations that it would without a.c. involvement. Your theory is not so absolute as you imply - for it to be valid, it has to agree with reality. You're taking certain extreme cases, and what you are saying about those is correct.
Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")
It is moisture inside the car, not outside that the defroster is removing.
I don't think anyone said that this wasn't the case. I/we just said that some car makers suggest running the AC in the winter. Never said that was a temperature below which it wouldn't run.
But it isn't this cold at ALL times during the winter, except in very cold parts of the country.
Well, I live in northern PA less than 5 miles from the NY border, and we are rarely below 25 or 30 degrees (the two temps I believe you mentioned earlier for R134a and R12 systems) for weeks on end or even days. Look at the average temps and you will see that they aren't far below these temps, which means that the highs are often above.
There are a FEW places like this in the US, but fairly few. You mentioned 6 states out of 50. Hardly and overwhelming majority.
I said winter, not below freezing. You are trying to put words in my mouth to support your argument. When you asked for a temp, I said 20F as I'm pretty sure that my AC has engaged at OATs in that neighborhood. You said that typical AC systems will not cut out until 25-30F. It may well be 25F under the hood when it is 20F outside, so this isn't inconsistent at all.
Why is it so hard for you to understand that it is the moisture INSIDE the car that is the problem, not the moisture in the outside air? Where do you live? It seems pretty obvious that you don't live anywhere that has a winter worth talking about as you seem oblivious to the issues we face in the winter.
Cold air can hold a fair bit of moisture, including in liquid form as supercooled droplets. And their is a phenomenon known as "winter fog" which forms at temps below freezing.
That's too bad, I was hoping on the second try you would get them correct.
Point is (stand up please so it does not go over your head this time)....for the snow to form, there must be considerable moisture in the air.
That is not what was stated, but obviously you will simply attempt to twist things to your satisfaction. I guess it is easier to some than admitting you are clueless on a subject.
Maybe there is a difference between not running the entire vehicle for two weeks or longer and not running the compressor for two weeks or longer, but it isn't obvious to me what the difference might be.
And the altitude of a Neon has what exactly to do with understanding the concept of dew point?
You do of course realize that at an outside temp of 20 degrees with the engine running the air temp under the hood on the fire wall (which is where my low cut out switch is located) does not stay that cold very long. I have had my compressors clutch engage down to at least a 15-20 degree outside temp and probably even colder.
I just posted an excerpt from my 2003 Caravan manual. While it doesn't mention winter specifically as I thought it did, it does mention running the compressor to insure adequate lubrication prior to leaving the vehicle for two weeks or more of "storage."
And on page 219 of the manual, it addresses the issue of the compressor automatically being engaged in defrost mode. It says, "NOTE: For improved safety, the compressor is activated and the recirculation mode is deactivated when Mix or Deforst modes are selected. This is done to assist in drying the air and it will help in keeping the windows from fogging."
It hasn't been obvious from his comments thus far and his seemingly lack of knowledge of how and why a car windshield can fog up in cold temps. He keeps talking about the dew point of the ambient air which has almost no bearing on the dew point INSIDE the car.
I'll check again this winter, but I'm fairly certain I've had mine engage down to 20F as I stated earlier. However, we're trying to confuse Neil with the facts, so we're likely wasting out time as facts seem hard for him to understand. And he likes to try to put words in your mouth to support his claims.
In their (the link you gave) description of how a voltage divider works, they repeatedly refer to the resistors in the divider circuit *dropping* voltage. The term "voltage divider" and "droping voltage" go hand in hand because a voltage divider works, by definition, by dropping voltage across the resistors to give the desired voltage at the junction. The sum of the voltages **dropped** by the resistors (2 in series in the classic voltage divider) has to equal the difference between voltage at the two extreme ends (i.e., V+ and ground in the classic circuit). V+ minus the voltage dropped by the top resistor gives the divider output at the junction. Also, by definition, 0 volts (ground) plus the voltage dropped by the bottom resistor equals the same junction voltage. Both resistors drop voltage, the sum of which equals the total voltage across the divider.
As a circuit designer of 20+ years, I can tell you that the more one works with circuits, including pure classic voltage dividers, the more one realizes that any load with a resistor in series with the voltage supply circuit is forming a voltage divider network with the series resistor. IOW, if you ask two designers if the ballast resistor/coil scenario constitutes a voltage divider, the neophyte designer will have to think about it and may in fact argue the point until the reality dawns on him/her. The exerienced designer won't even have to think about it - it is obvious to him/her because he/she has gone thru the mental realization at some point following repeated analysis of those types of cicruits that, for all practical purposes, the two situations (i.e., classical divider and a resistor in series with a load) are the same.
Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")
Basic High School electronics shop. By the way, next time you get a chance pop off the cover on that PC you are sitting at and take a look at the power supply. Perfect example of a large Voltage Divider circuit at work! Or if you want a smaller example their should be a number of them on the motherboard. Don't take my word for it though, perhaps some of these will help (I even included some that have pictures) :0)
You answer that yourself below. I made the mistake of assuming the the FSM would contain everything that was in the owner's manual and them some, so I only checked my '99 LH vehicle FSM. I just went out and looked at my '99 Concorde owner's manual, and see slightly different by similar statements that you see in your 2003 Caravan owner's manual.
Here are a couple of the several statements on the subject that I find in my Concorde owner's manual: "NOTE: The air conditioning compressor is on in this mode. This dehumidifies the air to help dry the windshield. TO improve fuel economy, leave in the defrost mode only when necessary."
"WINDOW FOGGING: In mild but rainy or humid weather, your windows may fog up on the inside. You can remove this fog by pressing the Defrost button. The Mix mode can be used to maintain a clear windshield and provide sufficient heating. If side window fogging becomes a problem, increase blower speed. The compressor will remain on during these conditions."
AHAH! So **technically** you *DID* mis-state the truth!!!!!!! 8^)
it does mention running
Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")
Well, maybe, but I'm 100% sure that I had at least one car that mentioned running the AC in the winter ... it just isn't my 2003 Caravan. :-) And, quite frankly, not running the AC in the winter months for more than two weeks at a time should be the same as going on vacation and not running the car for two weeks or more, right? At least I can't imagine any difference with respect to the AC compressor. I don't think it cares whether it is not spinning because the engine isn't running or it is not spinning because the clutch isn't engaged. So, even if using "winter" was technically incorrect with respect to the owner's manual, the advice was functionally correct. If I'm missing something here, please point it out.
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