How many cans of freeon does it takes before the compressor come on if it's out
It doesn't work that way. If the A/C system is low or out of refrigerant for the first thing, R12 Freon is nearly impossible to find, much less buy it. Any A/C system that originally used R~12 must be converted to R134, the gas now used in any system. It seems you are asking when the compressor will 'come on'...that has nothing to do with the compressor engaging for the clutch to run.
I don't think a '96 uses R12. To answer your question - the system should start cycling before the first can is completely in. A question: did you fix a leak or are you just pumping in Freon to try make it work? No Freon means that there is a leak. The stuff doesn't evaporate from a sealed, high- pressure system. The AC system could be compromised and several things need to be evaluated and addressed before you squirt any R134a at it. (Evacuate the system, change the receiver/dryer if it's been open a while, etc.) There should be a sticker to tell you how much Freon (R134a) to add to the system - a little math and some estimation will be in order but you can get pretty close. With High-side pressures approaching 350 psi, you're really better off taking it to a shop for an evaluation.
FIGURE OUT WHY IT IS LEAKING FIRST. AND DO NOT OVER FILL IT.
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