The kit consists of a short hose that is used to measure the pressure in the system, a pressure gauge, and an R-134 tap used to control the release of refrigerant from the cans of R-134 refrigerant. Sometimes the kit and refrigerant are sold as a package deal. I bought mine separately. The kit was around $18 and each can of refrigerant was about $6. One can will probably be enough, although if the parts place is any distance away, you will save a lot of frustration if you get two and return the second one later if its not needed.

Open the hood and turn on your a/c. The compressor on my 95 850 is on the left hand side of the engine compartment, the same side as the serpentine belt. The compressor is near the front of the vehicle and will spin and stop repetitively in short cycles of about five seconds or so if the pressure is low and more refrigerant is needed. In this area is a small vertical pipe with a black cap. Mine was only about 3 inches or so from the upper pulley of the serpentine belt, so watch your fingers! Mine had something like 6Nm written on top of it. This is the place you will connect your kit. Turn off the engine and take off the cap. Connect the tube and pressure gage to the nipple under the cap. Turn on the engine and the a/c. The initial pressure will be high, but as the compressor runs the pressure should drop. When the pressure gets low enough the compressor automatically shuts off. You should be able to watch the gage go up and down as the compressor cycles.

If the pressure is low, turn off engine, disconnect hose and attach the refrigerant to the hose following the directions with your kit. Attach the hose back to the nipple, turn on the engine and a/c. Open up the valve on the kit to allow refrigerant to flow into the system. The compressor should eventually stop cycling on and off. You should check the pressure on the system every five minutes or so. The pressure should be about 25 psi when the compressor is running. Good luck.