99 JGC A/C...easy question

I want to add some freon to my compressor, is the low pressure valve the one with the black cap?

Low Side is the bigger tube and will be cold to the touch. The High Side is smaller and is HOT!!!! to the touch. If it is R-134A to be added then the fitting from the can should only fit the Low Side Fitting. The High Side will be too big and will not fit the store bought add can setups. Only add gas which is can sitting upright. Do not turn the can upside down and add by liquid. When you add the R-134A the can will get cold. If it freezes up or gets too cold the Freon will not transfer to good. Let the can warm up and try to add more. Some people put the can in warm to hot water while adding. Please do not do that it is very unsafe thing to do. Standard temp out of ducts while running in MAX MODE is about 45 degrees. If the Jeep is hot inside you may only get about 60 degrees out of the ducts until the Jeep cools down some. Buy one of those pocket thermometers and put it in the duct on the dash to read the temps coming out. Be safe......and cool.

Oops....Forgot to tell you.....The HIGH SIDE is very high pressures so do not try to hook up the small store cans to the HIGH SIDE....Remember the Low Side is cool or cold to the touch.

even if its low on freon? would it still be cold then?

Depends on HOW LOW? If it's just a lil low 1/4 of a pound then yea it could still be cold but if it's a pound low then you will probably not have a very cold a/c system.

If it's real low the compressor will cycle on and off very frequently.