First, not sure where the low pressure port is on your model, follow the hoses and look for a fitting with a cap. The R-134 systems have different sizes for the low and high pressure ports, so it's the next best thing to idiot-proof. Low-side will likely be on the passenger side of the engine compartment somewhere.
Now, I have the same concerns as user NGM - bad things can happen to you if you aren't sure of what you're doing. The $50-$100 saved will look pretty small if you end up with a permanent injury. Eye protection is a must, face and hand protection are strongly advised.
I like to encourage people who have the initiative to do-it-yourself, but this is an area that one should get some better training other than the couple of paragraphs of instructions on the back of a kit.
1989 F150 XLT standard-cab shortbed 4x4, 5.0L, AOD, 3.55 gears, manual hubs, 31x10.50 tires, 218K miles. Repainted Oct09. SOLD - Jan2015
2014 F150 XLT standard-cab shortbed 4x4, 5.0L, 6-speed auto, 3.55 gears, auto hubs, locking diff, trailer pkg, 3K miles.