This all started as a merepublic service announcement
to new owners to check (or change) the oil in their gensets.
a paragraph here that explained that what follows elaborates upon the accusations of inattention to detail I made in the genset oil thread. It was obliterated by a sysop whose name I had dared to use to identify the individual to whom I was responding. I promise to never "personally attack" anyone on this board by such provocative action as using anyone's name again. Hopefully alternatives such as "hey you" and "that dude" will be considered non-belligerent.
Our rig was specified to have a 120 VAC system that included a shore connection (of course), a genset, and a 2800 watt inverter. The roof A/C was to be able to run from power supplied by any of these three sources, so we could air-condition our entire 24' Sprinter whether connected at a campsite (shore), driving down the road (inverter, with a high-current alternator), or out in the middle of nowhere (genset). This strategy was explained in detail to SMB before we ever put one dime down on the van or approved any design.
At delivery, I noticed an "extra" circuit breaker box wedged between the inverter and fresh water tank (under one of the dinette seats), and inquired about its purpose.
SMB: That's so the air conditioner will run.
Me: Why won't it run off a breaker in the load center?
SMB: The inverter won't let the generator start it.
Me: So what did you do to change the inverter's mind?
SMB: We put that breaker down there.
Me: So what passes through those extra breakers?
SMB: Power to the A/C.
Me: Power from what
to the A/C?
SMB: The generator...uhh...to the...
Me: Can I see the wiring diagram for the van?
SMB: [blank stares]
Me: Do you have a diagram of the van's 120 volt system?
SMB: [long pause] We...have a diagram of how to wire...an RV in general.
Me: [long pause] OK, but...everything works...right? Just as specified?
SMB: Sure, sure.
This nagged at me for the rest of the checkout process, and I kept dashing out to the van to rule out things that might NOT work due to whatever "detour" was taking place inside the mystery breaker box. My third suspicion proved correct: they had wired power to the A/C from shore and genset around
the inverter, so the inverter couldn't power the air conditioner.
Once I discovered this, they explained that this was because the inverter wouldn't "let" the A/C start. I voiced my (correct) suspicion that this was due to a well-documented protective function of the inverter--to interrupt power during AC under- or over-voltage conditions, and pointed out that the thresholds are easily adjustable in software. The inverter just needed to be re-configured to ignore the normal sag in voltage as the compressor motor starts.
We spent the rest of the afternoon sitting in the shop as they fuddled with temporary "test" connections, then returned the following morning so they could permanently remove their "extra breakers" and wire the coach as it should have been in the first place. With the inverter re-configured, everything worked as it should, except that the inverter (running from batteries, not just "policing" 120 VAC passing through it) would only intermittently succeed at starting the A/C compressor.
Sportsmobile shrugged this off as "oh well, whadda ya gonna do?" and even added that they have never
been able to get a true sine-wave inverter to power an air conditioner. Oddly enough, their (cheaper, cruder) modified square wave units will, which was the only solution they could suggest. I pointed out that modified square wave power causes motors to run hotter and die sooner, but again, all they could do was shrug.
It was left to us, after we got home, to research the problem (many hours), locate a solution (the SUPCO SPP6), buy it ($28), and install it (30 minutes). The hardest part, by far, was identifying the solution. This is not a new issue among RVers, though (the key info came from RV.com) and a competent builder of custom RV's ought to have been a little better informed.
I say this not as a figure of speech, but literally:
The guys who built our rig did not know what they were doing!
They didn't know (despite abundant documentation) how the inverter worked, didn't know how to adjust its software settings, and apparently didn't even know (or couldn't articulate) what their Rube-Goldberg workaround had done to make the A/C "work." Like a redneck with a Crescent wrench and a case of Budweiser, they just kept flailing around under the hood until they came up with something they thought we'd drive away in.
Further, they didn't even bother to know a simple fix (the SPP6) to a problem common to many of their previous customers!
I guess it was just easier to shrug.