I have type trane chilled water (centrifugal), when you turn it originally working oil pump, but chiller not working , noted the lock of oil when considering the lens on the oil tank down the pump, and no traces of lost oil, note that in the summer season, the chiller was working well, what is resson for not to return the oil to tank , is due to a malfunction in the (relief valve) as in the case of increasing the pressure imposed on the re-working oil tank again, or what reason do you think?