How can I fix my multimeter which consistently shows 0 for AC voltage?
The fuses are only  used for the current ranges and have no bearing for AC voltage measurements. Since this is a true RMS voltmeter, there is undoubtedly an IC inside which does the conversion from input AC voltage to a DC voltage proportional to the RMS value of the input. Since the meter works on frequency, the input AC circuits are probably OK. Since the meter works on DC, the DC measurement circuitry is also OK. Since the latter is also used for AC measurements, by measuring the output of the RMS converter IC, the most likely culprit is that IC.  You need to open up the meter and first look for obvious problems like burnt components or loose wires. Then try to identify the RMS chip. If you can get another one at a reasonable price, you can try replacing it. You could also try contacting the manufacturer of your meter to see if they could offer any assistance.