This is the first time i have to add some r-12 to my 89 mercury g/m ..can someone tell me which is the low side. One valve is on a little can on the back of the compressor. The other valve is on what looks like the dryer back by the heater box.
Thanks, gary

 

The low side (or Suction side) is on the dryer over there at the heater core area. Avoid the compressor, that is the high side and runs about 250 PSI (enough to possibly grenade that r12 can in your hand)

 

thank you very much. That is what i needed to know.