Recharging AC in 94 lesabre; HELP!

[mybuick]

I'm trying to recharge the refrigerant in my 94 Lesabre AC system. But I need some help, as I'm a do-it-yourself novice:
1. The product I bought is compatible with R-134a systems; my manual suggests mine is R-134 (no "a"); should I be worried?
2. I'm looking for the low-pressure cap and have narrowed it down to 2 possibilities. One on tubing running vertically (parallel to hood), the orher on tubing running horizontal (parallel to dash), both in the same general area near compressor. Any clues for dummies as to which is the right one?
3. Any other tips on avoiding disasters in the process?

THANKS in advance!

[Flatrater]

Your AC fittings are different sizes. The low pressure side is a smaller fitting on the larger line compared to the high side fitting

[HotZ28]

The Refrigerant Designation Numbering System

Because the chemical names of typical refrigerants are long and complex, a method of referring to refrigerants by number was developed by DuPont. The numbering system was released for general
use in 1956 and has become an industry standard. A complete discussion of the number designation and safety classification of the refrigerants is presented in ASHRAE Standard 34-1989.

Briefly, the method of designating a refrigerant by number is as follows. (Note that the numbering system begins on the right.)

First digit on the right = Number of fluorine atoms
Second digit from the right = Number of hydrogen atoms plus one
Third digit from the right = Number of carbon atoms minus one
(not used when equal to zero)
Fourth digit from the right = Number of unsaturated carbon-carbon
bonds in the compound (not used when equal to zero)
When bromine is present in place of all or part of the chlorine, the same rules apply except that the capital letter “B” after the designation for the parent compound shows the presence of the bromine (Br). The number following the letter “B” shows the number of Bromine atoms present. The lower-case letter that follows the refrigeration designation refers to the form of the molecule when different forms (isomers) are possible, with the most symmetrical form indicated by the number alone. As the form becomes more and more asymmetrical, the letters a, b, and c (lower case) are appended (For example, HFC-134a).
If all of the carbon bonds are not occupied by fluorine or hydrogen atoms, the remainder are attached to chlorine. Because the structure of a refrigerant, whether CFC, HCFC, or HFC, has become so important, they are often referred to in this way. For example, R-12 is CFC-12; R-22 is HCFC-22; R-134a is HFC-134a. This is simply a way of pointing out their chemical structure and therefore their relative
ozone-depletion potential.

[mybuick]

Thanks Flatrater, that's a big help!

[mybuick]

Wow, that's great info on the refrigerant chemistry--I really appreciate it!!