How do I convert or fill 92 Jeep Cherokee air conditioning freon?

If it leaks 134 it will leak R-12 .I have changed hundreds of systems over to 134 without any complaints. Don't let the 94% eff rating of 134a scare you because that does not mean that your ac system will lose 6% cooling ability .A large class 8 truck or maybe a high roof van black on black and poor insulation might tax the system in the 90% range on 100 degree days but most systems never get close .
134a high side pressure will be about 18% higher so most systems you need to change the high side cutout.The R-12 electric fan switch will be ok just make sure it is engageing the fan when the pressure comes up.You must check the condensor in front of radiator to make sure air flows easily thru it.On systems where the hoses screw on each side of the dryer I replace the dryer .Drain oil from compressor and replace with 134a oil .Replace that bad valve core (with ac valve core not a tire valve) Now very very important vaccum the system and if no loss of vaccum in 20 min charge with manufactors recomended amount of oil and freon.If a system is low on freon (cycling in & out on low pressure switch) you can add a pound of charge with those small cans of same type freon no problem but when there is a leak and the charge has been lost or changing freon types you must pull a vaccum to properlly charge the system. If you just charge R-12 or 134a your system will have traped non -condensables and a large drop in cooling ability. Hope this helps. Harold

R 12 gas and r 134 gas are different in the operating temperatures and the size of the cooling rad in front of the engine rad and compressor pressures but it will work
.are you using a proper air con machine or one of them weekend mechanic top up bottles which are about as much use as a haynes manual ,look on the credits of a haynes manual ??none of them hold a motor vehicle technicians exam --- I DO but their not worth the paper their written on when applying for a job because i done night school and not a university and mine are signed by a indian and in spain only spanish nationals can work for the goverment which means mine are no good from UK where any tom **** or harry can stand for parliament and work for the goverment now you know why iam so bitter ,right enough of that back to problem sounds like the adaptor you have have is not fitted properly if you can get one of these refill cans in R 12 then go for it because it will work far better as for the bolt heads you refer too i cant comment because i have never seen a R 12 air con on a jeep here only R134 but i cant see them being shut off valves and you wouldnt need to shut them anyway ,PS do the windows open??