This is a common problem of Robinair 34700Z / 347002k & 347112k series machine.so don't worry just check the following :- 1# Verify the ISV tank is not overfilled.if full,remove some refrigerant manually from tank. 2# Purge excess air from the tank manually.( Open air purge hose from the tank,then press tank valve as needed to purge air from the tank) 3#Check the air purge solenoid & High pressure switch for proper operation.Hope this will solve your problem, Best of luck & vote for my solution!

I have a 34700Z when i put it to vacuum it purge out the gas . i have change the purge valve but it does the same thing.