[MR2] reading a/c pressure gauges

[Kurt Krueger]

-------------- Original message ----------------------
From: tbamc <tbamc at gbta.net>
>
> I bought a used set of gauges for dealing with my a/c system, and 
> thought using them was fairly straightforward.  I then noticed that in 
> addition to a PSI scale, there is an R12 and an R22 scale.  I 'thought' 
> the large PSI scale was the one to use, but then seeing the vastly 
> different R12 scale I started to question that assumption.  Anyone know 
> the difference, or have a link to a site explaining it?  Google wasn't 
> kind to me.
> 

They should be vapor pressure scales, with a temperature scale on the dial too.
Here is a chart of vapor pressure of R-12:

http://www.google.com/url?sa=t&ct=res&cd=1&url=http%3A%2F%2Fwww.borderschess.org
%2Fr12.pdf&ei=qWxzSMvvKJGasQPCr8SiDA&usg=AFQjCNHgBO2j028WMAPv5dqD0v16Y5p_oA&sig2
=YjFAKD72BLpKeCRGiMa_IA


A simple explanation is if a liquid is in a closed container, the pressure
inside will be the vapor pressure.  In essence, the liquid boils away until
the pressure reaches the vapor pressure.  Note that this is highly
temperature dependent.  You can use the inverse of this
in the AC system.  If you know the pressure, the liquid should be at the
temperature corresponding to that vapor pressure.

My gauge set is buried somewhere, so I can't compare my gauge numbers to the
chart.