anyone convert from R-12 refrigerant to R-134 refrigerent on their older toyota pickup?

if so, did it work smoothly, did you have any problems with the conversion, and did you have to do anything special except screw on the new low pressure prot fitting, then add the R-134 into it [after you took all the R-12 out of course]?

I had it done on my 84.
The system must be completely evacuated first, R12 and R134 don't mix.
Then pull vac on it for 20-30 min to check for leaks.
Then add R134 and PAG oil.

I did it on my 83 as well. In addition to what fourwd1 posted, I would suggest replacing the dryer and possibly the expansion valve. Both are relatively cheap (assuming you're doing it yourself). Replacing the expansion valve will also allow you to clean out the evaporator (mine was about 80% clogged).