Sure, there are always multiple ways to work through a troubleshooting problem. But some ways are more straightforward, definitive, and less confusing than others. 

By saying that the converter fan should activate why you turn on the fridge, letting you know the charger is operating, implies that something is wrong if it doesn't, but in fact the opposite is true when you have a healthy fully charged battery.

And why wait 20 minutes to start the troubleshooting process when taking a minute to disconnect the battery and solar will tell you right away if the charger works or not? 

I did not state that this is the entire diagnostic procedure. It is not a shortcut, it is a first step, like the first go/no-go step in a diagnostic flow chart.

Weeel, you could attempt to shortcut the process that way but if the battery is fully charged to start with then the WFCO fan may well not come on for some time. Mine didn't when I tested this, even after 15 minutes. The fridge pulls about 10A, about 7 of which was coming from the WFCO and 3 from the battery. It would have taken significantly longer to get the battery voltage down to a level where the WFCO went into absorption mode and the fan turned on.   I had no solar connected.  

So, moral of the story is: avoid shortcuts in troubleshooting lest you wind up heading down the wrong path  and have to backtrack. Much better to run a definitive "no shortcuts" test of the WFCO, disconnect the battery entirely and see if the WFCO will run the trailer 12V loads. Takes just a minute or two  to do that. 

There is also a test done by Dave Hickey who attended the Kentucky MiniMini last October. He found that it was not necessarily vibration, but the screws for the grounding (marked FG) not being tight. Since the current that should be going through the FG screws cant, it then goes through other parts including the bridge rectifier which manifests as a cold solder joint on the negative terminal. Dave Hickey repaired a couple of bad ones while we were at the Kenucky MiniMini. We had a brand new one in the box that he used to take pictures for the guide he posted on the Facebook group last October:

WFCO 89xx Converter Field Repair Guide. Created by Dave Hickey.

In essence, one needs to check the underside of the converter's circuit board after disassembling to move shields out of the way and then looking at the rectifier solder points. If one looks burned, it is the problem one and needs to be cleaned up and re-soldered.

Of course, if the converter is still under warranty, don't do this. However, if it is out of warranty, it would be a lot less expensive than buying a new converter if it is able to be repaired. It wouldn't hurt to try.

volt fuses.

While on shore power, set the fridge to DC (battery mode)...set it for the coldest setting.

Within a minute (or as little as a couple of seconds) the converter fan should activate letting you know the charger is operating. If, after say, 20 minutes, the fan has not come on, and your battery monitor lights are showing less than full, it's certainly time to investigate further.

Confirm that the main fuses in the 12V distribution panel are good, and that the charger ac circuit breaker is closed. Then try disconnecting the battery and solar system entirely and see if your 12V loads will run directly on the WFCO. That won't hurt anything. If they do then your charger is working, if not then it has failed. In that case, I agree with Motor7 re Progressive Dynamics as a replacement.