I recently purchased a 1989 cherokee with straight 6 engine. I want to charge a/c with new r12 refrigerant. Ports are on top of compressor, which port is low pressure line. Left or right when facing from the front?

 

Are you charging it yourself or having a shop do it? If yourself, are you able to even get R-12 these days? Have you ever serviced an AC system?

Servicing this particular year XJ is a bit more complicated than "connect a can" and charge.

However, to answer your question, follow the line from the expansion valve on the firewall. It should go to the valve on the right side (looking at the compressor from the front). The high side line (on the left) goes to the condenser in front of the radiator.

 

There is an environmental safe R12 that can be purchased at Walmart.