I had a big long explanation for how and why a fuse should not blow, even in voltage spike situations, but when I hit "Post" ApplianceJunk
took too long to respond and I lost it all!
In short, the varactor should short any voltage spikes to neutral, saving all the other components on the board from being exposed to anything over 120V AC (RMS). The fuses are also protected.
The LG refrigerator board has a varactor, and two fuses. The fuse that is soldered blows during board failure. If the replaceable fuse blows due to voltage spike, this means the voltage protection circuit on the board is failing, and you should replace the board. This also means some components were briefly exposed to a higher voltage, which has weakened them.
A varactor can absorb high voltage spikes, but each spike reduces it's ability to absorb future spikes. If a fuse is blowing due to voltage spikes, then it means the board is failing.
The only way to know if a voltage spike has occurred is to look at past voltage data, which nobody has access to. If a serious voltage spike has occurred, then you will always see a blown varactor. This means the rest of the board is fried also.
There is a reason the manufacturers tell you to replace the board if the soldered fuse blows. I know they never explain why, and it is probably because they want you to buy the whole board from them, instead of replacing board components. My guess is they encourage buying the whole board because too often you can spend weeks trying to narrow down the root of circuit board failures, and it takes some pricey equipment to capture the failure. (digital analyzers, oscilloscopes, data loggers, etc....)
I used to work on flight simulators, and we had test equipment that got up to tens of thousands of dollars per piece. A few years after I left, the company spent $70,000 on a top of the line digital analyzer. This can be justified when you are working on hundreds of flight simulators worth a few million each, but in the appliance world. . . . . . . not even on a $25,000 AGA range.