a basic convertion from R12 to R134 will not yield temperatures cold enough for Texas or Arizona.
I was confronted a few years back into recharging and converting the AC system in a 240D. On a 110ºF day in Tucson temperature at the outlet was 38ºF on R-12; the conversion could never go below 50ºF. I rest my case.
Now with a renewal of internal components particularly that parallel flow evaporator... and R134 could work as intended (I have never had problem with the r134 system in my Nissan; Japaneses know how to make AC systems, germans dont!!!).