The Danfoss control module monitors condenser fan current. The difference between AC/DC could be related to the supply conductors for the DC side, but it's likely that the condenser fan is running outside the parameters of the module's program (<0.7A). The condenser fans are inexpensive (< $20), you can find a replacement on Mouser or other electronics supplier if you can get some specifics on the OEM fan, e.g. amp draw, cfm, dimension. Choose a ball bearing fan rather than a sleeve bearing, it will last longer and draw less current.
The Secop modules are also available from sources other than OEM, there is a model # on the module, match the front part of the number, the last 3 is the series. Most any module will work in a pinch. If you always have 12/24VDC available, you can save a couple bucks by using a straight 12/24V module and abandon the 120v connection altogether. \
The modules are very sensitive to voltage. If your supply conductors are even close to being marginal, increase the size of the wire. They do not like low voltage, so mind the voltage drop scrupulously.
If you cruise beyond easy reach of parts, a spare module and condenser fan should be in your spare parts inventory. If you have multiple Danfoss-equipped refrigeration systems on board, you can likely find a single module that will suit as a replacement for any of the units, keeping in mind a 12/24 module can be swapped for a 12/24/120 with no consequence.
