I have a problem with a parallel compressor system, hope that someone can help.

The system contains three compressors connected to common suction header and discharge header. Immediately after the discharge header, a oil separator is installed and the oil return pipe is connected to the common suction header. The compressors have features that pump out excess oil to the discharge header if oil level inside it is more than required. Compressor suction pipes are tee-off at the side (not bottom) of suction header to oil accumulation in idle compressor.

When three compressors are running, the one with longest distance from common header has higher running current and higher discharged temperature as compared to the other two. If only one compressor is running alone (ie. the other two are in idle), they all give similar current reading and pressure reading no matter their distance from the common header. I have experience with similar system but didn't face this problem.

Can any one give me advice?

Is there any article or book that I can learn practical design on parallel compressor refrigeration system?