Date:    Tue, 29 Jul 2003 08:41:13 -0700
> From:    "Mike D." <md03@XOCHI.COM>
> Subject: R12 or R134?
>
> I've got an 85 Westy, purchased about 4 months ago.   When first
> purchased, the AC worked poorly.  After being in the shop and not
> getting much driving, I recently discovered the AC didn't work at
> all.  It sounds like the compressor engages, but when I tested the
> valves there was no R12 pressure at all.
>
> So my theory is that there is a slow leak (6 months or so to fully discharge).

Bad theory! If you *fully* discharge, i.e. no pressure, in 6
months, that qualifies as a Large leak. Whichever way you go, you
should fix the leak first, 'cause it isn't going to get better :-)

And whatever else you do, *IF* you switch to R-134A, EVACUATE the
system first. While this is important with R-12, its crucial with
R-134A. The air in the system is non-condensable, raising the
already high head pressures, AND the PAG/Ester oils are
hygroscopic (i.e. they absorb water). The moisture in the system
can combine with the oils before being adsorbed by the drier,
resulting in poor oil circulation/lubrication, and compressor
going BOOM.

> So, any advice on the pros & cons refilling with R12 or converting to
> R134?  My theory is that if there is a slow leak, I'd rather be
> leaking R134 than R12.  Cost is definitely an issue, so the $40
> do-it-yourself R134 conversion is attractive (assuming that having a
> mechanic fix the leak and refil with R12 would cost hundreds of
> dollars).

A lot depends on where you live. Here in Phoenix (with temps of
117�F already this summer) R-134A is a bad choice. It does not
cool nearly as well as R-12, has significantly higher head
pressures (especially at high ambient temps), and is not miscible
with mineral oil (used in R-12 systems). At a minimum, when you
switch to R-134A, you need to replace the receiver/drier, drain
the oil from the compressor, and add the PAG or Ester oils used
for 134A. Any O-rings disturbed by the repair operation should be
replaced as well, as they are not compatible (undisturbed O-rings
should be fine, given the small amount of surface area exposed to
the system).

As for R-12, local Phoenix rates run $50-80 per can (actual cost
is $21-23 per can in case quantities), plus labor, if you have a
shop do it. You can expect to be charged for at least 3 cans for
an empty, evacuated system, and you'll have to find a shop with
R-12 Recovery/Recycle equipment in order to service it.

Unfortunately, both choices are kinda ugly. If you live where
temps are less than 100�F, then the R-134A may work fine. There
are some good R-12 replacements (like Freezone, FridgC, etc.) but
the downside is finding someone with the recovery/recycle
equipment dedicated to that material the next time you need a
repair. So far, I'm sticking with R-12, waiting for a better
option.

Keith Hughes