this chiller is a 134a system and is going out on excess surge. what is causing this machine to surge. the 134a system don't have a purge unit, the pressures don't never get below atmospheric pressure. and its making a loud noise at the condenser (rumbling noise). not used to working on a 134a machine so anyone have any suggestions? usually i would say it would be air in the system but like i said it keeps pos. pressure during the off cycle so air cant enter.