HH56 wrote:
You need a valve sized to fit the fitting and line as well as the cubic inch capacity in the evaporator -- although most auto and aftermarket evaporators today are about in the same CI size range. I don't how successful you will be in finding adapters but the AC place you are dealing with would probably be a place to start.

For a normal car the typical hose or line sizes are #10 for the suction side which is about 5/8" tubing, #8 between the compressor and evaporator at about 1/2", and #6 from the evaporator and receiver/drier to the expansion valve which equals 3/8" tubing. If there is a long run from the compressor/evaporator side or more than one evaporator core then each of those sizes often go up by one size. I believe #12 or about 3/4" is as large as it gets for automotive use. A larger size line than standards will not be detrimental in operation but just costs more. Too small is though because if on the feed side, it can result in refrigerant starving in the evaporator and too small on the suction side and the evaporator could flood because refrigerant cannot return to the compressor fast enough.

There are also metric and proprietary fittings which I know very little on how they would correlate to the SAE or other AC standards.