I have a 98 blazer and the a/c clutch is not engaging. How can I fix this problem so my a/c will work

 

You probably have a leak in the system. You could get one of those charging hoses and a can of R134A at autozone, but I wouldn't recommend it. You SHOULD have the leak diagnosed and repaired by a professional with the proper equipment, because the system will never reach maximun cooling capacity without first fully evacuating it to rid it of any air.