Neon AC compressor cycling

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

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.

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?

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.

Still waiting.

um, Clare...

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

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)

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;

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.

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

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