There are two valves of different sizes 1 high pressure and 1 low pressure. You should see two silver tunes coming from the radiator are usually on the passenger side of the car follow those ac lines and each one will have a valve on it. There should be a cap on each one. Most cars have them near the front of the car but on occasion they have been on the back by the firewall.
Answers & Comments
There are two valves of different sizes 1 high pressure and 1 low pressure. You should see two silver tunes coming from the radiator are usually on the passenger side of the car follow those ac lines and each one will have a valve on it. There should be a cap on each one. Most cars have them near the front of the car but on occasion they have been on the back by the firewall.