If there is and where is the orfice tube in the ac system of an 89 ford f-150 with the 300 inline 6. the system has been evacuated and the lines pulled, but still no orfice tube, and another thing, its an r-12 system that is being converted over to r-134a. other than the orfice tube, is there anything else that is a necessity to change on a budget...the fittings have been added...and like said before, the system is evacuated...just asking before it is recharged???