Compressor start-up problem

[Z. Kan.]

An Emerald 60,000 BTU duct type air conditioner was operating well since it was installed from about 3 years.

Actually, the compressor isn't starting up when powered through the backup diesel electric generator.. It's like the contactor is going on and off at a period of 0.5 sec.
Please note that the air conditioner is still operating well when powered through the 250 KVA transformer.
The Phase to Phase voltage of the generator is 380 V, while it's about 415 V on the transformer. (Which are both included in the rated operating range of the air conditioner).

I noticed a voltage drop to 312 V on start up when powered through the generator; this problem is actually not present when working on the transformer, nor previously even when the generator is in operation.

Can anyone help me resolve this problem please?

[JWWebster]

In the biz they call that Chatter. the contactor is "Chattering" Prob a bad solenoid coil on the contactor.

Note: If you have 24 volts operating the contactor how far is the run from the transformer to the contactor? If it goes from down in the building up on a roof ya might not have a big enough transformer especially if you are using a backupgenerator.

[dave@orion]

obviously the voltage drops below the rated as the compressor draws current to start. i would check the control voltage at the contactor .

[Icehouse]

You answered your own question by stating the voltage DROPS