Don't know if it will help but on GMC autos they used a orafice tube instead of an expansion valve. If you left the original tube in the vehicle then it would do just like you say but changing to the next size smaller orafice made them cool just sitting at idle. The tubes are color coded and availible at autoparts stores even autozone type places. Just don't expect the guy at autozone to know anything more than what his computer tells him. Some Ford cars also used these orafice tubes.

Also some places supply an expansion valve of a different pressure setting for R134A. Supposed to make some systems work better. Basically the pressure setting on those valves is what is used on factory autos with R134A. Somewhere I have a catalog with them in it, but right now I don't even know where to look for it.

If you have an expansion valve then you won't have an orafice tube. Those pressures are way too high. About 230psi on the high side and 20-40 on the low is a full charge on most any new factory system. On out tractors and combines I ussually only charge to 190psi high side and get good cold air.