It uses R134A. Before you go out and buy it, you should first unbolt the housing over the heater and evaporater cores and check to make sure the evaporator core is not plugged with dirt. Very common problem. There are four screws on the top front of the cover, four screws on the bottom rear of the housing and two or three along each side. Pull the cover free and rotate it and lay it on top of the cab.
Have someone listen if the compressor clutch kicks in when you turn the key on with the air conditioner swtich on and the blower on low speed. No need to start the engine to check this. If the compressor clutch does not click then you are totally out of freon or you have another electrical problem. The low pressure switch is up by the evaporator and drier. See if you have power at both termials.
If the compressor is continually cycling on and off with the engine running then you are low on freon. The system does not hold much freon, so you need to be careful you don't add too much and cause the high pressure switch to cut the compressor out.
