Neon AC compressor cycling

Well, it's been a couple of years since Clare claimed that a
ballast resistor is a voltage divider, I asked him; "where the
voltage is divided to?"

Still waiting.

 

That's OK, he's never had a carload of just-off-ice hockey players in
his car at -25C. They is plenty o' humidity there! And you are sure
glad to get some dehumidification from the AC.

And I know it happens, especially in the first gen. Neons because you
can feel the AC compressor engaging when your are cruising along the
highway.

Dan

 

Most manufacturers have the A/C engage when the car is in defrost mode.
Chrysler is one of the only ones that will not light up the a/c light
though. Ford, GM, hyundai, and honda all do. It is incorporated in the
design of the HVAC system.

 

Typically, old wives tales aren't writting into owner's manuals from
reputable companies.

Air can hold enough water vapor to form fog at subzero temperatures.

I'm a pilot and know a fair bit about dew point. I know enough to know
that clouds can form at temps well below freezing. Read up on "airframe
icing."


Matt

 

What's "low enough?"

Matt

 

Incar temperatures far above frezing, and outside temp of well below
freezing, underhood temps well above freezing, and yes, the compressor
DOES come on with the heater in the defrost position, or with the AC
turned on in the recirculating mode. Can not vouch for coming on in
standard fresh air mode, but I'm sure it has. (on my New Yorker and on
the Trans Sport

 

A standard ballast resistor in series with an ignition coil IS a
voltage devider. The coil sees part of the voltage, the coil sees the
rest. Get a voltmeter and try it. Or to be SURE you can see it, get
two. Put one meter across the resistor, and one across the coil, and
ground the negative side of the coil (like closing the "points").
You will see, on a typical system, (lets say on a vehicle using a Napa
IC107 coil and its associated resister) 5 volts across the resistor
and 7 volts across the coil with 12 volts supplied.
If you are still waiting for the answer it's because you didn't read
your mail back then.

 

That is *exactly* how air conditioning lowers humidity - it cools the
air before it gets to the heater, even more moisture condenses out (that
"dew point" thing), then it gets heated up, so you end up with even
dryer warm air. It might seem that cooling it only to have to heat it
again would be counterproductive. However, the reality is that under
many situations, the total effect of pre-cooled and then heated is
greater than simply heating if the purpose is to keep moisture from
condensing onto the windshield and decreasing visibility (it's a safety
thang).

The only reason that the mfgrs. put a limit on outside temperature
before the compressor is disabled is to protect the compressor from
damage. Otherwise, the a.c. would be allowed to run in defrost mode at
the colder temps.

In most geographical areas, a.c. inherently runs enough during the
winter months to get the benefits to the compressor that Matt talks
about from being in the defrost mode - I mean it is not *always* below
the compressor lockout temperature, and certainly not for months at a
time. And for those places that are that cold continuously for months
at a time, well, that's life. Point is that a benefit that serves most
of the owners very well is derived.

Years ago, when a.c.'s were not as common in autos, and the controls
were truly manual without computer over-rides and complex algorithms,
and the a.c. was not integrated into the defrost mode, the manufacturers
indeed did advise the public to run the a.c. occasionally during the
winter months for the reasons Matt cited. With the automatic operation
in defrost mode, it isn't necessary to give that advice, and you don't
hear it anymore, and the public is less informed about the situation
altogether (i.e., very few people are even aware that the compressor
runs automatically in the defrost mode, even if they know what a
compressor is).

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

 

Yep - the load (coil) acts as the bottom resistor (in the traditional
schematic of a voltage divider). Didn't even have to explain it for it
to be obvious.

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

 

Well what do *you* consider low enough. I know from my years in New York
that that the compressors on my newer vehicles engaged when in the defrost
mode even in some pretty damn cold whether (as in well below freezing).

Certainly isn't *DRY* ice coming down! Where do you think all that moisture
that is creating the snow is coming from...the humidity in the air. When
humidity level and dew point meet ...viola! moisure. Warm temp = Rain Cold
temp=snow

It certainly helps clear any fog/frost that may have formed on the inside of
the glass and defogs much quicker.

Likewise

 

For some of the thick skulls on this group explaining it, with
pictures (like a comic book) isn't even enough.

 

"southerners" should not pretend to be authorities on things they know
nothing about - like winter, and heaters, and frost. And they
(particularly if non pilots) should not advise pilots on things like
dew point.

 

Typically, old wives tales aren't writting into owner's manuals from
reputable companies.[/QUOTE]

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.

Okay, good. At 20 degrees Fahrenheit, the pressure in a R-134a
system will be 18.4 PSI, a typical R-134a system low pressure cut
out switch will open at 22 PSI, for an R-12 system at 20 degrees
Fahrenheit, the system will be at 21.0 PSI, a typical R-12 low
pressure cut out switch will open at 26 PSI.
Guess what isn't going to happen at 20 degrees Fahrenheit?

Well Mr Pilot, what -is- the maximum altitude ever achieved by a
Dodge/Plymouth Neon?

 

What's "low enough?"[/QUOTE]

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.

 

Incar temperatures far above frezing, and outside temp of well below
freezing, underhood temps well above freezing,[/QUOTE]

Can't help ya Bub, these conditions can only possibly exist on
Clare's planet. Go back to the part where you claimed "heavy
condensation on the windshield/backlight when you leave the car
sit?"

No fucking wonder that you have a problem with windows fogging
up...

Sure Clare, what ever you say...
Just take those laws of physics and chuck 'em right out the
window.

 

Still waiting.

um, Clare...

Dropping voltage doesn't mean that it has been divided.

 

That is *exactly* how air conditioning lowers humidity - it cools the
air before it gets to the heater, even more moisture condenses out (that
"dew point" thing), then it gets heated up, so you end up with even
dryer warm air. It might seem that cooling it only to have to heat it
again would be counterproductive. However, the reality is that under
many situations, the total effect of pre-cooled and then heated is
greater than simply heating if the purpose is to keep moisture from
condensing onto the windshield and decreasing visibility (it's a safety
thang).[/QUOTE]

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)

So you're agreeing with me that there is a point in temperature
where the AC compressor is not allowed to run because the system
pressure would be so low so as to lock the compressor out.

Well, I'm sure that Steve Lacker can get plenty of use out of his
air conditioning during the winter -months- but that is not the
question, the question concerns winter -conditions-, i.e., cold
temperatures, cold enough that the ambient temperature puts the
system pressure below the low pressure switch's cut out point.

It is in Wisconsin and Minnesota and Michigan and North Dakota
and Montana and New York and Alaska and probably quite a few
other states not to mention large parts of Canada.

Yes, it's called -WINTER- which is a big part of Matt's original
premise.

You mean where it's warmer and not below freezing which was not
part of Matt's premise.

oh, okay.... I guess I missed the part where Matt's post was
directed at owners of much older vehicles.
Seen many 1962 Dodge Noens?

Well now, Matt says that they -do- give that advice and now
you're saying that they don't.
I'll side with you on this one but do me a favor, check the
owners manual for your Concorde and see if there's a specific
recommendation about running the AC compressor in the off months
to keep everything lubed.

One last thing... On those old cars where it was recommended to
run the AC in winter, why is it that evaporator freeze up (as in
blocked solid by ice) was not a concern?

Is it possibly because under winter conditions, there wouldn't be
enough moisture content in the air for it to be a concern?
(round and round we go)

 

Well what do *you* consider low enough. I know from my years in New York
that that the compressors on my newer vehicles engaged when in the defrost
mode even in some pretty damn cold whether (as in well below freezing).[/QUOTE]

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.

So the 90+ inches is -inside- the vehicle stuck to the windshield?

Probably because you jump from one thing to another.

 

Did I remember to mention that 'dropped' voltage is not the same
as 'divided' voltage. (yes I did)

here guys;

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

scroll down about 1/3rd of the page.

 

Good advice Clarence, too bad I live in Wisconsin and learned to
fly back in the 70s.

On the other hand, if you know the maximum altitude ever achieved
by a Dodge/Plymouth Neon, please tell us. Otherwise, you're
still as full of shit, still as washed up as you always have been.