Short answer.
Long story short.. If you found the tube where the orifice tube goes into (the one on the evaporator) and its not there and hasn't been opened since the system worked you blew it into the evaporator.
Long Answer...
Been there done that..
Years ago, the A/C was working great.. next day nothing. I hooked up the manifold gauges and found no pressure drop across the orifice tube. I pulled the line off and voila.. NO ORIFICE TUBE.
I called a neighbor (mechanic) of mine and asked him what to do.. He told me it depended on how good my karma was.. He suggested I throw another tube in there, evacuate and fill it.. and just remember that my evaporator now has an orifice tube in there too. I did that and the a/c worked..
Fast forward many years later..
While working on the new upper front shock mounts I got a little happy with a grinder and hit the evaporator box.. which mean I let a bunch of green gas and goop out.
I bought another evaporator, orifice tube and acumulator (figured, why not).. I patched the a/c box and changed the evaporator and accumulator and put in the new orifice tube. While charging this system everything was going well then I heard a loud pop and then no pressure drop.
Yup.. I blew another orifice tube into the evaporator. I looked at what was holding the orifice tube in and it was just a couple (yes, 2) tiny dimples on the line. I took a pair of channel locks and made more/deeper dimples while being careful to keep the tube round. I then put in another orifice tube, evacuated it, charged it and the a/c is still going strong (only a couple years later so far)..
We use Variable orifice tubes which give you a bigger pressure differential so I don't know if that had any bearing on it...
~Mark
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