I just installed a new AC compressor in my '94 Explorer and was wondering how many 12oz cans of R134a it will take to fully charge the system. I've put in one 12oz can of oil and 4 cans of R134A. The compressor is running and blowing cold air, but there isn't much pressure in the system.
There should be a sticker up by the fan blower somewhere, that will tell you how much to charge. R134a and R12 charge amounts should be close to equivalent. I've heard they work best with 80% the recommended amount when converting to R134a. My '92 took about 3.5 cans. Typically, you want to charge 'em up to where the compressor doesn't cycle. If it blows cold and doesn't cycle on max AC with the fan turned up all the way, it's good. More pressure is not good.
12oz. is plenty of oil. Your compressor will let you know if it's not.
There are two service ports on teh AC system, The high pressure or liquid side and the low pressure vapor side. Freon is added to the low pressure side and when running the low pressure will vary between 20 and 35 PSI, this is normal. If it appears that there is not much pressure and your looking at the low side while the AC is on, this is normal. When the AC is turned off and the high and low side equalize, the reading on the low side will be higher. Be carefull not to overcharge the system. Sorry for the long winded reply.