Sorry for the delay, been outta town driving the bus.
You wouldn't be the first guy to have one of those little cans blow
up in your face. Usually it's from people connecting the can directly
to the high side. Charging with a manifold set is not normally done
with the little cans but there is no reason you can't do it, just be
sure the last thing you do is check the valves. I realize you needed
the low side valve open but remember neither valve needs to be open
to check pressures. This is a continuing confusion among people new
to A/C work.
It gets even stranger about the retard marking, it refers to what's
called the "retard protection" built into the gauge. It's the range
beyond the normal working pressure (above 120psi on the compound and
above 500 psi on the high side) where the gauge span is changed to
protect it, to permit pressures beyond the normal range without
damage. Most newer sets have 200 to 500 psi of retard protection
depending on the gauge.
It's to alert the user that the reading is out of range and can be
much higher than the position of the needle would seem to indicate.
(If you look closely you might see the PSI scale jumps to a higher
number in the retard area).
Why is it called retard protection and marked as retard? I honestly
don't know. It's not common to older gauge sets. You aren't the first
guy to laugh about it though, the common joke is it was an attempt to
develop an unbiased grading system for A/C techs. It's claimed to
indicate IQ after attachment to the system the tech is servicing ;)
Neither of my sets have retard protection markings although my
analyzer (www.digi-cool.com) does has retard protection. Leave it to
you to stump me on a detail. Now I'll need to find out exactly why
they call it that, I only know what it does.
As always, feel free to visit at www.aircondition.com for advice or
www.acsource.com for goodies. For example Nylog is great stuff, you
should get a bottle.
> So I look at my low side manifold gauge and notice that the upper
end has an area designated "RETARD". I laughed my ass off. Yeah, if
I let it get that high then I'm definitely a retard. So what
is "retard" really supposed to mean?<<