Neon AC compressor cycling

Okay, you've got five or six sweaty guys breathing hard from
exertion, exactly what does this have to do with ambient humidity

You had the AC set on 'recirculate' on Clarence's advice?

 

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")

 

All well and good Bill, but we're talking about a situation where
the ambient air temperature is already low and the dew point is
so low that there is very little moisture content to begin with
(like Matts 20*F cite)[/QUOTE]

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")

 

Did I say that Matt is an evil person, or is this an act of
desperation?

That's exactly what I did, state reality.
Unfortunately, old wives tales and egos got in the way.

The reason that you didn't find it is because the OEM can't be
certain that the AC will run in winter conditions if they make a
blanket statement that it will. At 15* F and five people in the
car exhaling moisture which is then collecting as fog on the
windshield/windows, the AC will not run and it will not aid or
assist in clearing fog from the inside of the windshield/windows,
and before you claim "extreme cases" be advised, it's a common
everyday occurrence in the northern states during the months of
January, February and December.

No argument from me on that. But do try to understand, (simple
as it may be) it is a question of whether there -will- be
involvement, not whether it will be beneficial when there is.
I have not nor would I ever claim that AC does not assist in
defogging vehicle glass. i simply made two points to correct
erroneous beliefs; 1) the AC compressor will not always run if
the temperature is cold enough, 2) ambient humidity eventually
gets to a point where AC assisted defogging is not an issue.
I can't help it that a gaggle of weak tits trotted out all manner
and species of red herring in the form of airplanes, altitude,
snowfall, heavy breathing/sweaty hockey players and how their
1969 Rambler Ambassador behaved.

Um... It was Matt who proffered the absolute, I was merely
correcting him.

Well Bill, just come to Wisconsin in the dead of winter and I'll
be glad to point out all the cars driving down the road with
fogged up windshields and windows due to the fact that below a
certain temperature, the vehicles AC will not run because the
pressures are too low to allow compressor clutch engagement.

 

For the benefit of those who haven't taken to inventing their own
definitions;

http://www.allaboutcircuits.com/vol_1/chpt_6/1.html

 

All well and good Bill, but we're talking about a situation where
the ambient air temperature is already low and the dew point is
so low that there is very little moisture content to begin with
(like Matts 20*F cite)[/QUOTE]

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.


Matt

 

I've posted the numbers in another reply, so I won't be repeating
them.

Um, no... You claimed that cold air does a pretty good job of
holding moisture. Snow is not moisture held in the air, it has
already precipitated out.[/QUOTE]

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.


Matt

 

Which says exactly what Bill said above. Where does it say that two
resistances in series does NOT constitute a voltage divider?

Matt

 

But then being from Wisconsin I'm sure he must have already known that!

 

I've posted the numbers in another reply, so I won't be repeating
them.[/QUOTE]

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.

Just trying to keep up with you Mr. Wizard!

 

Of course not... which is sufficient reason for me to retrieve
the owners manuals from both my 95 Dakota and 98 Intrepid.
No mention what-so-ever in either owners manual WRT running the
AC system in winter for any of the reasons that you cite.
Since Bill Putney has a vehicle almost identical to one of these,
I invite him to check -his- owners manual to see if there is any
mention of running the AC in winter to keep the seals lubricated.[/QUOTE]

Well, I just pulled the manual from my 2003 Grand Caravan. While I
didn't find a reference to winter specifically, on page 234 it has a
section titled "Vacation Storage" that says:

"Anytime you store your vehicle, or keep it out of service (i.e.
vacation) for two weeks or more, run the air conditioning system at idle
for about five minutes in the fresh air and high blower setting. This
will insure adequate system lubrication to minimize the possibility of
compressor damage when the system is started again."

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?


Matt

 

For an R-134a system, 25 degrees will put the system pressure
below the low cut out switch's trip point, for an R-12 system, 30
degrees will put the system pressure below the low cut out
switch's trip point.

System architecture will usually have either a low pressure
switch mounted in a low pressure line under the hood, a
evaporator temperature switch mounted in the evaporator case or
in the case of the Neon (and many other Chry-Co vehicles) both
wired in series to the compressor clutch.[/QUOTE]

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.

 

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.


Matt

 

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.


Matt

 

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)

http://www.yourdictionary.com/ahd/v/v0142400.html
http://www.tpub.com/neets/book1/chapter3/1-35.htm
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/voldiv.html
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/vdivac.html
http://www.doctronics.co.uk/voltage.htm
http://www.electron-tubes.co.uk/accs/dividers.html
http://www.semiconwell.com/r_net/swrv.htm
http://floti.bell.ac.uk/principles/series_circuits/sld007.htm

 

Bill, it is clear from both this thread and the AC thread that, to use
an old phrase, we're mud wrestling with a pig.


Matt

 

"No" to both questions.

What I meant by that last sentence was that I expected to find at least
two things at least touched on by the FSM:
(1) A list of conditions under which the compressor can run beyond the
obvious "when the operator pushes the snowflake button" (one of which
would be that the defrost mode is selected), and
(2) Some over-riding factors, such as at what tmeperature or what
combination of conditions the compressor would be locked out when in the
defrost mode.

I expected those things to be mentioned in a beginning-of-section
description of the heating and a.c. system and/or a troubleshooting
section (criteria by which to tell if the system is functioning
correctly or not. All that I could see mentioned is that the compressor
is turned on and off by the BCM (meaning all the answers are in the
firmware algorithm), which would be useless info. for troubelshooting,
short of a totally dead BCM output.

At 15* F and five people in the

No argument from me.

BTW - you can force an honest-to-goodness degree symbol in any text
document by holding down the Alt key and punching in 0-1-7-6, then
releasing the Alt key (the numbers must be punched in on the numerical
keypad part of your keyboard - won't work with the numerical keys above
the QWERTY keys. I keep a whole list of such codes (ASCII codes) next
to my computers at home and at work for technical writing that I do for
a living.

A couple more favorites of mine: ± (alt+0177), Ø (alt+0216), µ
(alt+0181), ñ (alt+0241), ¡ (alt+0161), ¼ (alt+0188, ½ (alt+0189), ™
(alt+0153), • (alt+0149), § (alt+0167), ¹ (alt+0185), ² (alt+0178), ³
(alt+0179). No charge for that info! 8^) Theres a couple hundred
more, but those are my favorites. No ASCII code for the ohms synbol,
omega, that requires a "W" in Symbols font, or certain other fonts like
Greek (duh!). Oh yeah - I also use í (alt+0237) - comes in handy on
forums for words like naíve), and á (alt+0225) for voilá!. 8^)

And you come to humid, moderate-temperatured Virginia and I will show
you the opposite. 8^)

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

Their definitions and mine are the same.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")