Air Conditioning

getting hot here in ohio. lol. when i bought the cherokee the ac didnt work. however the people i bought it from did work. i jumped the compressor directly and it kicked on. also i checked the relay and it is in good condition. the last thing that i figured it would be is the low pressure switch. is there a way to test how much pressure is in it? can that switch fail? is there a way to add refrigerant to the system myself. its a 94 4x4 sport. 4.0 auto. the haynes book i have says that 95 and newer uses the r134a refrigerant and the 94 and older uses the r12 or whatever it is. but on the radiator support it shows it as being r134a. any help on this matter would be appreciated. thanks in advance.
patrick

You more than likely have the r-134 system. There are some "over-the -counter testers" that are supposed to tell you how much you have(freon), but the only way you are going to know is to find someone with either a set of gauges, or the actual machine that will leak test your system and check the operation of your compressor. The reason its not coming on is probably due to either a low charge or no charge at all. You can look for a leak yourself by looking at all the A/C fittings, valves and compressor, looking for a wet/oily area. 134 used a green dye, that you can see with an ultra-violet light and UV glasses. Hope this helps some.

thanks. im going to take it to my buddy who has a machine. i guess he will hook it up and see whats wrong with the charge. does anyone know how much psi there is supposed to be in the system. i think that i read somewhere that it should be around 100 psi. but im not sure.
thanks guys

A/C systems use high and low pressures. A good operating system will generally be about 28-35 low side and 200-230 high side. This is also affected by the ambient temp.