Are you talking top off or full recharge after opening system to do
a repair ?
R 134A can become dangerous if " oxygenated " *** Never use
compressed air to test a R 134A system *** That's why the special ACME
valves . For starters use a Pressure guage to determine if system holds
pressure, if it's flat, you need serious servicing, if it's down a bit,
use a can tapper to add R134A to * Low * side. The Tapper is a few
bucks at any auto parts store, along with the R134A which you can buy
without a licence. The pressure guage may be a bit hard to find,
try a big auto parts store, or a dept. store with a big auto section.
Florescent dye can be purchaced in tiny cans that connect to tapper,
add to low side with compressor running, you might want to short
low pressure switch [ on accumulator ] to get compressor running if
system is low.
For serious AC service, you need an evacuator, plan is to draw
vacuum on system for at least 1/2 hour to remove air and moisture
from system. Failure to do that will result in system icing up
[ water vapor ] or blowing up [ oxygenated R134A ] .
If you only want to keep your AC in top tune, get it evacuated and
recharged by a " good " shop. Write down outside air temperature, and
pressure indicated on guage. Later on, on a day that's the same
temperature, check pressure with guage, add R134A until pressure is same
as when car left shop. Air temp affects pressure, since I suck at math,
I go with " same temp " readings.
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