Have an old 91 cherokee, does anyone know proper procedures to refill ac?

Question

I heard you have to decompress/unfill it before refilling with refrigerant. Does it take more than one can? My manual does not say is there a site or something to reference?

Answer 1

You will need to take it to a shop to have the R-12 refrigerant evacuated from the system if there is still R-12 in it.  Then while they are doing that they can do a leak test, which usually involves filling the system with a non-toxic environmentally safe gas, usually nitrogen, to check for leaks.  If there arent any leaks install a R-134A retrofit kit and have them fill the system with the updated refrigerant.  

I am a licenced technician and have a licence to handle refrigerant(required in canada) and im not condoning this but there is a product known as r-12A which is a hydrocarbon blend.  It is safe for use in automotive AC systems and is cheaper and safer for the environment than R12 and R134A.  a bonus is you dont need a license to buy it.  The kit comes with a fill tube, and 2-3 cans of refrigerant and a sealer(dont use the sealer).  Make sure if you use this you get your system evacuated and leak checked at a proper shop before you put the r-12a in if you choose to use it.  The R-12A kits come with detailed instructions in the package and on the bottle.

Answer 2

Without the proper equipment you really can't do it right.

You need a big air compressor capable of sustaining 75psi under load for an extended period and the appropriate vacuum system and gauges.

Without the proper equipment and ability to use it , simply follow the instructions on the can of freon and add a can of the compressor oil while you are at it.

Answer 3

91 model you need to check and see what kind of refrigerant it uses. I bet it takes R-12 unless its been switched over all ready. I don't think they started using the new stuff(R-134A) until mid 95 models. Now with that said you can not buy the R-12 you have to have licenses to  buy it now. You can not mix the 2 together are you have more problems. It should have a lable some where under the hood on what kind it uses and how much it takes.