Has your home had 2 or more exterior AC condenser/compressor units? If so, there is a good chance your circuit breaker may be too large. Older units sometimes required 60+ amp breakers. Newer and more energy-efficient units may only require 25 - 30 amp breakers. Near the bottom of this picture, the data plate displays "max fuse/ckt brk 30 amp". Check the data plate mounted on the side of your outside unit and compare it with the size breaker installed in your main breaker panel. If your breaker is oversized, you need to consult with an electrician because you have a potential SAFETY HAZARD.