The mail man just dropped off the 110-12 control board, and it has two burned spots on the back at two relay connections.
What I bet happened is that it failed in service, and when they installed the new one, the old one got saved, just in case they needed parts from it. They wrapped it in the packaging that the new one came in, and it was eventually included in a municipal surplus sale. Whoever bought it probably didn't unwrap it to get a closer look – it was wrapped in an ESD bag. I'm willing to give him the benefit of the doubt, particularly since Hoseline is very oddball to work with if you haven't run into it before-
Regardless, even at the purchase price of $59, it was well worth the price. New relays will cost me $6.96 per each (Digi-Key Electronics), and that way, I'll wind up with a rebuilt module for a LOT less than the $390 that Hoseline gets for a new module. Thankfully, these relays meet an ISO standard, so the numbers on the top of the relays are all that I needed to match them up.
There are two identical relays – they handle the main condenser fan, one for vehicle power, and one for shore power. Since they both do the same job, I'll replace both, just in case.
It's a 70 amp relay, so I figure that either it got contaminated (doubtful – the board is way to clean), something short cycled the relay, or (my own favorite idea) – someone coupled both a primary and a secondary condenser to the “Condenser” terminal, instead of to the “Condenser” and “Secondary Condenser” terminals. The board came from North Carolina, so a primary and a secondary condenser makes sense. Hoseline usually puts a single condenser on a 40 amp fuse, so two condensers could completely load / overload a 70 amp relay.
Par for the course – one or two steps forward, one or two steps backward. The relays are on order, and it will take longer to remove the old relays than to install the new ones. I'll open up the failed relay to see if I can see what caused the failure.
With this board, I can build what I need. Instead of having this board control the whole AC system, I'm going to just have it control the 110 volt portion through a separate thermostat (labeled Shore Power AC, or similar). Both systems can control the same blower by letting the shore power pull in a relay to transfer the relay to the shore system.