Can I bypass my ac pump with a smaller serpentine belt

you can either do that,or remove the a/c compressor and install an a/c bypass pulley and use the original belt,that's on it now.dorman part number is 34166 a/c bypass pulley.if you want to leave the compressor on,instead of using the bypass pulley.get a tailors tape measure and measure around all the pulleys,except the compressor.start at one pulley,go around all pulleys with tape until you come to the last one,this is how long the new shorter belt will need to be.Example:now,you have a 855K6,which is an 85.5 inch belt.now it will be what it measured,for instance an 80.5 inch belt,which would be an 805K6.the belt is about $15.00 cheaper than the bypass pulley.if you don't have a tailors tape,do it old school with a small rope or string,and just mark it with a marker when you get to the start point again.