doubts

I have a fiat siena 1300 which presents a fault when I turn on the air since it brakes the engine to which this is due to the engine is done has two months it slows me so much that the direction is made hard to me. I thank you to who can help me

The first thing is to check the A/A compressor, surely it is dry, without oil and when it begins to work, suffer an reheat and principle of grapse. I doubt it is a motor problem. Remove it and throw it the oil that can take a small washing with new oil you throw it again, then add the amount established by the manufacturer and mount it.
All brands have a drainage and reputation screw of the oil.
That is going well.