Re: AC

[Robert Myers <rmyers@wvit.wvnet.edu>]

---snip---
>Michael, 
>  Yes the refrigerant is under pressure.  Anywhere from about 60 psi on the
>low side to about 300 or so psi on the high side. Can't remember exact
>numbers right off hand.  

>Air will only enter the system if there is enough
>of a leak where the pressure in the system bleeds off to atmosphere.  There
>are a couple of reasons to make sure the air is evacuated from the system
>before recharging with freon.

Sorry.  Bzzrrrrt.  Not (totally) correct.  Agreed, freon, under high
pressure, will effuse out of small leaks faster than air, under
comparatively low pressure, will effuse in through the same openings.
But...  air will effuse in at the same time and the same openings (but not
at the same rate) that the freon is effusing out.

If the pressures are equal, air will effuse through an opening faster than
will freon.  Rate of effusion is inversely proportional to the square root
of the molecular weight of the gas.  Freon has a significantly higher
molecular weight than either oxygen or nitrogen and will therefore effuse
through an opening slower than the "lighter" air.

The result of a slow leak is that the freon leaks out and air leaks in.
But, the two processes are occurring simultaneously, not consecutively.


___
	Bob 
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