Mazda Repair: A/C service, thin pipe, pressure gauge

Question
On the '93 Protege with the four liter engine.  Which is the low pressure line, the fat pipe below the thin one coming through the firewall? with the valve on it?  I got a retro fit kit with three cans of R134A with a short hose with a quick connect fitting on one end and a fitting with a pressure gauge built onto it for tapping the cans of R134a.  The directions aren't very clear on identifying the low pressure pipe and valve, nor is the diagram that came with the kit. The system had hardly any freon left in it, the reason it wasn't doing its job I suppose. I presume the thin pipe is the high pressure since it goes accross the engine and around to a sight glass with some plugs with wires then on under the radiator and I suppose to the condensor.  Am I right in guessing which is which?  

Answer
Hi Robert thanks for asking.
The high pressure line is the line comming off the compressor going staight to the condensor, the other high pressure line will be the one coming off the condesor to the expansion valve on the fire wall, or it will go to the receiver drier. it is usualy the thinner one that is the high side, But it doesnt really matter on which side you charge it on,
good luck
Chris P