[Richard]

Four pounds of 134a is about right for the dash system. Your low side switch should not be cutting out at 30. It should cut out around 15 to 20. Can you jumper the switch or run a 12v hot to the compressor to force it to run long enough to get lo and hi readings? I can think of several possibilities. One, you have a huge leak and don't really have 30 psig when the compressor is running. Two, you have too much in the system and the hi side switch is cutting you out. Three you have a clogged expansion valve.