Hi to everybody...

I'm now driving merc w126 280se.every morning when i started the car i can feel the engine is running well.but when i driving to town with a/c everything is fine.when i came back to house before i shut down the a/c the engine is look like running so slow if i turn off the a/c is more bad,i can feel my car whole engine look like wanna shut down.i open the bonnet and check all of the fan belt everything running so slowly also the engine shaking...Anybody can help me for this?????This car is Automaticis not manual