Using a GOOD digital thermometer, have it installed at the pass side dash AC duct. Run the RV at 1200 to 1500 RPM's and on MAX cool(recirc). Have someone WATCH the thermometer. Then slowly add the 134a. The output temp will then slowly drop. Once the temp gets to a low temp and stops going lower and then starts to RISE, stop the fill. You have reached the saturation point. Just blindly adding 134a is not a good idea. Also, do NOT add any oil to the system. NOT NEEDED. Doug