[Vwdiesel] 2000 TDI a/c question - and a brief description of the A/C sys...

LBaird119 at aol.com LBaird119 at aol.com
Thu Jun 3 23:24:08 PDT 2010

In a message dated 6/3/2010 11:01:59 PM Pacific Daylight Time, 
tonyandlillie1 at earthlink.net writes:

> You have a gas in the A/C system that gets compressed by the compressor 
> whenever the compressor is engaged via the compressor clutch. When it's 
> compressed, the temp goes up. This increased temp is then above ambient 
> temperature, and some of the increase is removed int eh condensor that sits in 
> front of the radiator. Then the compressed gas is fed into the expansion 
> valve, which releases it into the evaperator. This has been reduced sufficiently 
> in the condensor that it can now drop the evaproator to a very cold temp. 
> After that, it leaves the evaporator and gets pulled back into the 
> compressor.
  Maybe it's semantics but it's not a temp increase that causes the 
heat release and absorption capacity, it's change of state.  You 
compress a gas and it becomes liquid.  Compress it more and it'll go 
solid. When you have a change of state (solid, liquid, gas) you get 
a release or absorption of heat.  (See:  Is hell exothermic or 
endothermic.)  :-D
  Compress the gas and the increase in pressure causes it to turn 
to a liquid, thus releasing heat.  That liquid then meters into the 
evaporator, where the pressure is low enough for the liquid to 
boil into a gas.  Metering is done with a capilary tube or expansion 
valve typically, however mostly refrigerators, window a/c's etc 
use the capilary tube.  Chevy uses/used(?) a POV system that 
uses basically two expansion valves.  One meters liquid into the 
evaporator, the second meters gas OUT of the the evap. to maintain 
a set pressure level inside the evap.  Maintain a certain pressure 
and you maintain a certain temp. Thus no freezing up and maximum 
cooling.  My Audi 5KTD uses this and it works GREAT.

  When the gas boils, it absorbs heat (you heat water to make it  
boil) and then "carries" that heat to the compressor where it starts 
over again.  
  Large systems use a "slop tank" to catch any liquid from "slugging" 
the compressor and ruining it.  Just in case any liquid continues out 
of the evap.
  (I think I'm right about all this)  :-D

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