Air ride compressor coming on a lot

98 explorer limited
How often should the air ride compressor be running?
seems like mine is coming on an awful lot and for longer more recently, which sounds like this might be expensive.
 
 

Best thing to do is check your air lines for leaks.  The compressor should only come on when the pressure is low.  Hopefully, that will be your problem, and should be a fairly inexpensive repair.  The next thing is to check the air bags or shocks for leaks.