On Fri, 5 Aug 2011 09:19:28 -0400, "Flying Pig"
wrote:



So, I'm about to commence recharging. I'll post the results here, but
expect something similar to Vic's experience, in the end.


Not sure which "experience" you mean.
But to clarify my experience, it's not extensive and only involves
fixing maybe 6 or 7 auto A/C's.
When an A/C stops putting out cold air I first assume a leak of
refrigerant.
The gauge set confirms that.
So far every time with R134a.
In the old days of R-12 I didn't have a gauge set and just injected
in R-12 until it blew cold.
If it lasted less than a summer I replaced the compressor.
No evacuation, just replace the compressor and charge with R-12.
Did that twice with 100% success..
R134a leaks faster - smaller molecules than R-12.
With the R134a I've always had a gauge set.
But I've found that published exact high and low side pressures are
somewhat meaningless.
Pressures can easily be off 10 psi on the low, and 20 on the high side
and the system works fine.
That might indicate something on some systems, but it never told me
anything on the automotive systems I've fixed.
The gauge set makes you feel like a "pro" and is real handy for the
manifold.
I've found that if you just add the specified weight of refrigerant
you're probably there.
I stop injecting after the weight spec is met.
Even that's not exact. For example my Chevy Lumina calls for 34
ounces. The cans I use are 12 Ounces.
So on the 3rd can I'm guessing.
What I do is use a temp probe in the vent, make sure the system has
stabilized to the lowest temp, and after about half of the last can
inject in 15 second intervals, watching the temp.
When it doesn't change I stop. But I always end up closer to 36
ounces than 34. I don't fret about that.
Likewise, before I bought a good evac pump, I didn't always bother
with evacuating either. Used an air-operated vac pump a few times
but they don't pump down as needed.
Never noticed anything untoward, but auto A/C's don't have the long
lifetimes expected of boat and home A/C's.
Cars die pretty quickly, especially when they're 6-10 years old when
you buy them, which is what I do.
So far none of my A/C fixes have gone more than 6-7 years before I
junked the car/van.
The main advice I have is to refill with a dye.
If you leaked the refrigerant you need to find the leak.
I do maintain one car with 134a that just needs a can added every
couple years, but that's the only one I've seen like that.
And I don't expect to have that car much longer.
All the others have lost their charge much more quickly so I've
learned to just put the dye in and find the leak.
For me it's usually been compressor seals. One time dryer o-rings
that weren't rated for R134a, and twice condensers.
Luckily no evaporators.
From your descriptions, unlike a car, the parts that might leak are
hard to get at, and the system is different than an auto's.
Bottom line is R134a dye and a good UV light has *always* worked
for me to get at the heart of the problem.
But I've had it easy, and can't tell what you face from here.
Good luck and keep us posted!

--Vic