Q: The A/C works only when the fuse has been replaced in order for it to continue to work. What causes this?

It is important to know which fuse you are replacing. Is it the fuse to the compressor clutch or to the blower motor to be precise. Either way, I can give you some insight that you can use to figure this out.

Anytime a fuse blows in a fashion such as this, it is an indication there is a problem with the primary component in the circuit. When an electrical device such as an A/C compressor or a fan motor turn on, there is an initial spike in current. As components begin to age, this spike can, but now always, will begin to increase due to a resistance in the system. The resistance can be electrical or mechanical. Both will cause an increase in the amount of current needed to start the device.

Since you said the heater works, but not the A/C, I assume it is the compressor clutch circuit that is blowing the fuse. Which ever circuit it is, the most likely cause of the problem is the compressor clutch or the blower motor under that dash. Before I replaced either of these, I would test the actual current of each device in addition to a visual inspection of both systems. Bad connections will require a higher current for a circuit and a bad connection can occur anywhere in the effected circuit.

If you decide to get this fixed, consider YourMechanic, a a certified technician can service your fuse issue and ensure that everything functions properly. Be sure to send the mechanic a note explaining how the fuse continues to blow intermittently.

Good luck!