My car engine lags when i switch ON the AC.The RPM drop a bit.My car was quite old but i found the same situation in modern cars also.Except on modern cars,the RPM will be adjusted to normal by ECU.I know that when i switch ON the AC,the clutch at the compressor works.But i wonder whats the relationship with the engine lagging?Does the compressor drains a lot of current from the battery?