Troubleshooting a Danfoss BD35

[Sonosailor]

It is a Danfoss BD35, air cooled. We arrived back to the boat on the hard, after leaving it for 6 months, and are trying to troubleshoot it here in Grenada while we search for a professional.

Symptoms are:

1. The compressor gives a one-second shudder every four seconds. It does not otherwise run, hum, or vibrate.

2. No cooling effect, obviously.

3. The fan leads from the electronic controls provides 9-10 volts for the 12 volt fan, but the fan does not move. Fan has been checked and runs fine closer to the battery.

What should I try?

[Dsanduril]

Well, if either Richard or Rich pops in they can give you lots of advice, but I'm going to bet that the first piece will be to try temporarily wiring the compressor direct, with good sized wire, to a fully charged battery. If it runs with new wire connected direct to the battery then the problem is voltage drop somewhere in your wiring system (which seems the case since you only see 9-10 volts at the fan).

Only other option I can see is a locked up compressor, do you have an ammeter in the system? Can you see how much current the fridge is drawing (even if other things are also on you should be able to tell by turning the fridge off then on and watching the difference in current flow)?

[Sonosailor]

Finally found the problem. A switch on the negative side was not fully contacting. Old school research, and "Always check the Negative side too!"
Dsanduril: I did work through some of your advice, but my wiring still included the problem switch (too short). Ultimately the solution presented itself when similar problems were showing up in other electrical apparatus.