Philip,
We're talking about two different controls. There are sensors, or in older
cars, capillary tubes at the evaporators monitoring evap temp to control
what you're talking about, evaporator icing. In late model cars that also
cycled the compressor as that was how pressure/flow of refrigerant was
maintained. But there is also an ambient temp sensor that would not allow
the compressor to run below a certain outside air temp in order to prevent
hydraulic lock-up of the compressor due to refrigerant being in a liquid
state in the comp head. Refrigerant "boils" and becomes vapor at a low
temp, that's one of the reason it's used as a refrigerant. If the temp
drops below that "boiling point" on the low pressure side the gas will
condense back into a liquid and hydraulicly lock up the compressor. I
mentioned the diference in the refrigerants as a possible explanation for
why the posters old lincoln a/c would run at temps below his late model
mustang, however I was simply stating that the American government didn't
regulate this 40F cutout, the laws of physics did.
Steve.
"Philip" <1chip-state1@earthlink.net> wrote in message
news:4nQxd.6785$yK.4838@newsread3.news.atl.earthli nk.net...
> Has nothing to do with the refrigerant. Has solely to do with the
> temperature water freezes at ... 32 degrees. Since in most cases, all air
> flows thru the evaporator and then to or past the heater core, were the
> water on the evaporator be allowed to freeze solid, no air would flow out
of
> any of the plenum chamber outlets.
> --
>
> - Philip
>
> "Steve G" <NospamforSteve@Steve-Garner.com> wrote in message
> news:0ZOxd.534980$Pl.108826@pd7tw1no
> > The low temp cutout may have different settings, but that is most
> > likely a result of the diferent refrigerants used, r12 vs 134a,
> > Your 83 may still run at 40, but there is a temp close to that
> > where it will no longer engage. They all had low temp cutouts for
> > the very reason I mentioned. Or, the low temp cutout may have been
> > by-passed or is not working properly. Take it out on a cold frosty
> > morning and run the ac and let us know what happens.
> > I'm a mechanic by trade (inter-provincially licensed) and worked in
> > the field in the 70's and 80's and never saw a compressor cycle in
> > temp below 35 to 40 F. Up here in the frozen north of Canada we
> > use our defrost a lot and they would engage the compressor in the
> > mild weather, but have never seen a compressor run in the cold.
> > Not sure what it has to do with buying a 3 gal toilet tho...
> > <MajorDomo@mailcity.com> wrote in message
> > news:41C78DD7.991EF9E3@mailcity.com...
> >> You certainly are entitle to your own opinion. The AC on my 83
> >> Continental will run below 40 degrees but not my 2005 Lincoln LS
> >> or my 2003 Mustang GT. Go try a buy a three gallon toilet or a
> >> new model top loading washing machine in the US today.
> >>
> >>
> >> mike hunt
> >>
> >>
> >>
> >> Steve G wrote:
> >>>
> >>> No it's not!
> >>> AC systems have always had low temp cutouts on them, and it's not
> >>> idiocy for the above poster. The ac is called for anytime the
> >>> defrost is selected on most cars but is prevented from cutting in
> >>> below 40 F because below that temp the gaseous refrigerant will
> >>> liquefy and as we all know you can not compress a liquid. It
> >>> cuts it out so that your compressor doesn't smash to little bits
> >>> trying to compress liquid refrigerant.
> >>> Short lesson in refrigeration, compressor draws in low pressure
> >>> gas, pumps out high pressure gas. High pressure gas condenses
> >>> into a liquid under pressure in... what else but the condenser
> >>> (that other rad in the front of your car). High pressure liquid
> >>> is metered/sprayed into the evaporator where it becomes a low
> >>> pressure gas again and so on.
> >>>
> >>> For the OP, cars with persistant high humidity situations
> >>> sometimes have water leaks that may not be apparent. I had a
> >>> Supra that leaked water
> > at
> >>> the hatch. Windows seemed to fog easily. Discovered one day
> >>> that the spare tire well was half full of water.
> >>> Steve
> >>> <MajorDomo@mailcity.com> wrote in message
> >>> news:41C78298.78A50057@mailcity.com...
> >>>> The deactivation on newer domestic and automotive AC's, at 40
> >>>> degrees, is a federal regulation intended to save energy. Same
> >>>> as the limit on water capacity for toilets and the latest washing
> >>>> machines sold in the US. Your government at work.
> >>>>
> >>>>
> >>>> mike hunt
> >>>>
> >>>>
> >>>>
> >>>> "Gary L. Burnore" wrote:
> >>>>>
> >>>>> On Mon, 20 Dec 2004 15:43:59 -0500, Abeness <news@nada.x> wrote:
> >>>>>
> >>>>>> C. E. White wrote:
> >>>>>>> Unfortunately most A/C systems don't run once the
> >>>>>>> temperature drops below 40 degrees Fahrenheit.
> >>>>>>
> >>>>>> I don't believe this holds true for automotive systems. On my
> >>>>>> old Pontiac the A/C was directly tied to the defroster
> >>>>>> setting--switch the system to defrost, and the A/C was
> >>>>>> activated.
> >>>>>
> >>>>> It depends on the make/model. My cressida shuts the A/C off if
> >>>>> you turn the inside temp past 75%.
> >>>>>
> >>>>>> Good way to keep the compressor oils circulating to keep the
> >>>>>> seals lubricated, in addition to removing condensation. Worked
> >>>>>> at any temp, as I recall, and I move around NY/New England.
> >>>>>
> >>>>> It does help with condensation. There's no doubt about that.
> >>>>>
> >>>>>> I'll confirm this on my new 94 Civic in a few days, as it has
> >>>>>> now gotten cold enough around here to check. Disabling it
> >>>>>> below 40 degrees would be idiocy--it's the only way to remove
> >>>>>> condensation effectively.
> >>>>>
> >>>>> I'm pretty sure that even in his case, it's the temp you set the
> >>>>> control to and not the outside temp.
> >>>>>
> >>>>>> It is true, however, that many room A/Cs don't function when
> >>>>>> the outside temp is "too low"--which occasionally annoys me.
> >>>>>
> >>>>> There's a way to fix that, put a plastic bag over the outside
> >>>>> of the A/C after poking several holes in it. (The bag, duh).
>
>