Your low side fitting will be on the drivers side between the dryer(40 oz size black container with site glass on top, hi and low pressure switches connected to it) and the expansion valve. Should be very easy to see, looking from front of engine right side just above fender well.

I would not add freon without checking pressures as you may add too much and blow a seal.... Even if you don't blow a seal your AC will not work well with too much freon as well as with too little.

You need to monitor the high side as well. It is located drivers side in front just under the radiator hose about 12".

Just hooking up gauges will tell you a lot, also make sure your aux fan is coming on.

Good luck

Anthony Bridges