APC in row cooling unit compressor problem

[Abdelsamd.Mostafa]

Hello dears,

An APC in row cooling unit (ACRP 102) was showing up some alarms as flows,

1- Compressor drive fault

2- High suction pressure

3- relay output abnormal

And we tried to troubleshoot this problem several ways so we moved the unit's drive to another unit and it worked normally.

So i concluded that the fault is keep showing up because of the Compressor.

So we changed the compressor, filter dryer, and the expansion valve.

And the unit back to life and worked normally for about 45 days.

But unfortunately the same previous alarms back to show up again ,so we tried to change the drive, and same alarms exists.

And we noticed that when the drive begin trying to start the compressor, there is a sound comes out of the compressor shows that it is trying to start but it doesn't make it.

I have checked the winding resistance and it was 0.3 ohm , 0.4 ohm and 0.6 ohm ,also i have checked that the compressor is not grounded, and it was ok.

Also the suction & discharge pressure are equal (931 kpa)

I have attached the charging meter to the suction and discharge port and i found it equlaized too (that means that the sensors are good and working normally)

So what i am asking about, what it is the problem of the unit?, and what should I do more to know it ? and to be shure about my diagnosis?,

Also if i will have to change the compressor again what are the possibilities that may cause the compressor damage? And what should I do to prevent such damage to happen again??

Thanks in advance.