it's impossible to tell over the internet what is overloading the circuit.
best thing to do is have a mechanical contractor investigate the problem.
DON"T KEEP CHANGING THE FUSES!!! you will likely destroy the unit. best thing to do is have a tech check out the system. if the unit runs when you change the fuses, the repair should not be massive.
The TRUE highest cost system is the system not installed properly...
Do you go to a boat repairman with a sinking boat, and tell him to put in a bigger motor when he tells you to fix the holes?
I am yourmrfixit