It's been really hot here lately, and the A/C in my 1999 cooled a little but the compressor cycled on and off every couple seconds. I had trouble deciding if I should take it in for service (i.e. $125 at Sears) or try charging it myself ($30 for a recharge hose with a low side pressure gauge and 12oz of r134a). After a lot of research and questioning the folks at a local garage and parts place, I finally caved and bought a kit.
The charging hose was the type that had a fitting that screwed onto the refrigerant can and had a trigger to release r134a into the system and a pressure gauge to measure the low side pressure. The pressure is only readable when the trigger is released and refrigerant is not flowing.
The refrigerant was plain r134a. No "cool booster", no high-mileage, no UV leak dye, and absolutely no leak seal.
When I first hooked up the hose before I started the engine and ran the a/c, I thought the gauge read 0 PSI, which I didn't really think about much. I started the engine and turned the A/C on full, and the low side pressure was cycling between about 50 PSI when the compressor started to about 25 PSI when it cut out dropping while the compressor ran. I turned off the engine, and the gauge read over full scale at the high end, past the red danger zone! A little research on the web seemed to indicate that when the system is off, the entire system could have 100 PSI in it. Maybe I misread the gauge when I first hooked it up.
Anyway, I proceeded to recharge the system. With the hose disconnected from the low side port I screwed the bottle onto the hose. I didn't have any problem with any refrigerant escaping. Then with the engine running and the A/C on I connected the hose to the low side port. I waited a second or two for the compressor to cycle on and pulled the trigger on the valve. The can got cold in my hands while the r134a flowed into the system. Over a period of 20 minutes or so, the period of time the compressor stayed on got longer until finally it stopped cycling off. When the last of the refrigerant left the can, which I could tell by the temperature of the can in my hands, the low side pressure stabilized at about 35 PSI. The temp here tonight is about 80 deg F.
I would say the system could probably use a little more r134a based on the gauge reading and the current temp, but I'd call it a big success! Just thought I'd share.