2001 maxima intermitent a/c freeze up problem

[reever]

HI: My auto a/c problem is described below:.......what is the problem do you think? 2001 nissan Maxima a/c was empty this spring so my mechanic filled it with a can or two of R134 and added some sort of stop leak stuff. HE measured the R134 fluid content so it was the right amount put in....... Now my a/c works in city driving all the time but after driving for about 20 minutes on the highway with a/c on at high.... or low , the smooth running fan starts to make a muffled missing /clicking like sound and the air flow reduces to 5% of normal or less. If I stop and open the hood the frost is caked on the tube very thickly. If I stop the car or turn off the a/c during the highway drive for 5 minutes , the a/c comes back on again when I hit the button, but returns to the above bad performance within 5 minutes or less. We have adjusted downward the amount of R134 fluid in the system several times , still within the recommended levels of the gauge but with no improvements in operation . Also, we have cleaned out a few things in the system. Any ideas as to what the problem is? Thanks, Bob

[jwerty1]

too much r134have someone use a ac service machine to properly measure what you put into itif it works normally in town and then freezes up, this is about the only thing that could cause it, unless your compressor never cycles off