Hi trying to figure out why the engine vibrates a lot when i put On my Ac on my 97 Civic with Ac off its fine . Iv changed out all Mounts still no luck the vibration resonates thru the steering and all the way to the muffler. Any ideas were should look?

 

Make sure the condenser fan works. If the condenser overheats the pressure rises and the compressor will put a lot of strain on the engine. Same thing happens if the system is overcharged with refrigerant or oil.

The idle rpm should increase slightly with the A/C on. If it drops, you may need to clean the IACV or even open up the air screw.

 

The condenser fan works fine and the idle sits at 600rpm when off and 900rpm when on and it stays steady there. My first thought was mounts thats why i changed them but that didnt help