Brother of the Benz
In determining what line is what, remember that the low or suction line is the larger of the 2 and returns from the evaporator/dash to the compressor. When the A/C is operating this line will be cold. The discharge is the smaller of the 2 and goes from the compressor to the condenser. This 1 is HOT.
Your charging hoses must have valve openers.
If you are capabile of servicing your unit, and considerring the cost of R12; you may consider changing to R134A.
The change over is quite simple and very inexpensive, $29.95 at K-Mart. This includes 3 cans of R134A, 1 can of oil charge, a can adapter and charging hose with excellent instructions.
My W124030 does quite well with R134A.
Happy Trails Beep Beep from The Spiderman in Houston!!!