YORK Chiller Air Ingress on Shutdown

[imranmd]

Hi,

We are facing air ingress problem on one of our Centrifugal York chillers Model No. YTH3J3E35COG, 500 Tons with R123. Last time we found some leakage in the solenoid purge valve on the purge unit which was afterwards rectified. The purge unit was separated from other system and Vacuum was held for 24 Hours in both systems. After this satisfaction the gas was charged and chiller taken in service. After purging air from the system during the operation, the chiller worked fine at 0 purges/hour for the last 40 days. however when it was turned off, the condenser and evaporator pressures started to increase gradually and after 2-3 days time the condenser pressure reached 14.7 PSIA. Which shows an air ingress in the system.
The problem is that the air ingress problem comes only when the chiller in non-functional (in off state). While running there in no air ingress and no purges. Can someone identify the root cause of this problem? Please let us know the efficient and quick way to detect the leakage.