So here I am working on painting my boost stripe in the boat yard yesterday when I get the same type of call I get almost weekly, it goes like this:
Client: Hey Rich, I need to buy a new compressor/condensing unit, mine died.
Me: Can I ask you why you think your unit is dead?
Client: ya, it won't start up and my dock
neighbor knows about refrigeration came over and said it was dead.
Me: Do you mind if I ask you a few questions and give you a few tests?
Client: Well, ok. But my buddy is an expert and already did all the known tests.
Me: I'm sure he is, but just humor
me. So can you first run a temp DC power line right from your battery
plus and minus terminals to the black box controller on the compressor?
Client: man, that's a pain in the ass and I checked voltage with my volt meter at the unit and it says 12.3v and my volt panel on the ships display says 12.9v, so I don't have a voltage issue.
Me: I understand it may look that way, but trust me, I go through this all the time and I don't want you to buy a new compressor/condensing unit if you don't really need one.
Client: well ok, I will do it, but I'm telling you, my boat has the most beautiful wiring
you have ever seen. It just can't be my million dollar boat's wiring
Me: well do the test and call me back even if it's a Sat or Sunday I will be here.
Client 45mins later: Well I'll be damned...when I wired the unit straight to the battery
it fired right up, I can't believe it. So then I started looking around and found that the power panels
ship ground was loose and when I fixed that, now my unit works. Thanks a lot for saving me $1495 on a new unit!
Me: You are welcome amigo....now back to painting.
That's the norm....
The problem is (as Richard points out) there is no in the field test to see if your controller has failed/burned out and died. You have to arrive at that determination by the process of elimination or by swapping out a known good controller.