Here's a chart for pressure versus ambient temp. http://www.ackits.com/aacf/ptchart.cfm Notice how much the recommended pressure varies for 134a. In my Opinion the biggest problem with conversions is running too high a pressure to compenstate for the fact that 134a doesn't cool as well as R12. The good thing is that Deere somewhat oversized the system to make up for dirt and air leaks so a conversion will work. First thing is to ignore the sight guage. If you fill the system full enough to clear out the bubbles then the system is too full and you'll eventually find out where the weak points are in your system. I try to run as low pressure on the high side to just get the job done and spend my time keeping the evaporator and condensor as clean as possible.So keep the drain lines for the evaporator clear so that it doesn't get mud forming up there. Make blowing out the condensor part of the front axle greasing. Keep the seal between the evaporator and the top plate in good shape to not allow air to by-pass the evaporator.