The A/C Pro is a DIY air conditioner recharge kit that retails for about $45 to $50 for the canister and recharge hardware. The hardware includes a recharge hose with low side port connector, pressure gauge, and refill trigger.
The first step is to locate the air conditioner's low side port. This port's location will vary from model to model, but A/C Pro maintains a catalog of port locations on its Web site. The A/C Pro's connector will only fit on this port, so there's no chance of accidentally connecting to the wrong side of the system.
Before recharging, there are a few more things to check. First, make sure that the car is running and that the A/C system is running. Now, check that the compressor is actually spinning. If not, you may have bigger problems than this system can fix. Finally, attach the A/C Pro's connector and measure the current pressure of the system. If it's low, begin the charge.
After removing a safety collar from the A/C Pro's canister and twisting the canister into place, pull the trigger and begin the recharge. Shake and rotate the can while charging, and periodically stop and check the pressure level to avoid overcharging. You may notice that the can will get extremely cold while recharging, so maybe wear gloves while doing this.
The A/C Pro's pressure gauge features a rotating overlay that should let you estimate the proper pressure level. With the center of the red "V" shape pointed at the ambient temperature, fill the system until the level falls between the two red lines.