Hi All, when i start my octavia mk2 2.0 TDI AT the rpm is 750, and when i switch ON AC, rpm is rising to 1050 during idle, after i drive few kms, it become normal again. Pls let me know what would be reason, i recently replaced EGR aswell. 

You are increasing the demand on the engine,

and the battery load and the vehicle is responding by increasing the rpm and charging the battery and producing electricity for the load demand.

In your case the AC requires the engine to work harder,

similar as when you turn on lights, up the heater fan, rear screen, heated mirrors, even turn the steering when stationary or moving slow.

Edited 3 December, 20178 yr by AwaoffSki

you're correct, it demand more work for compressor, steering and alternator..  but my 180000kms of journey it never happened for AC.. i know if i switch on lights, around 50rpm will rise. but not for AC even it take more load than alternator .this is happening for last two weeks only,that too only  initial ideal period, after some time it is coming back to 750rpm..

 I'm presuming it could be regeneration process, but that should happen in ideal not while i switch on AC..