With the unit unplugged:
Look for the two connectors that are sticking out of the flue (round tube on the right looking from the back). They should have wires attached. remove the wires.
Using a test meter set on ohms (resistance) measure the resistance of the element by placing a probe on each blade connection that is sticking out of the flue.
If you have max resistance it signifies an open circuit or burnt out element. If the resistance is low (100-500 ohms IIRC) then the element is ok.
The refer has to be removed to replace the element but the element replacement is a cheap fix compared to the cost of a new unit.
Most of the major RV repair places will have some, not camping world, they will want to sell you a whole new unit. I would call around locally, if they don't have it they should be able to order it.
WBCCI #5501 AIR # 49
1978 Argosy 28 foot Motorhome
Wise men talk because they have something to say; fools, because they have to say something. -- Plato