Unable to get Generator to power Air Conditioner

You are underestimating the startup current demand on the Dometic 13.5. It can be in excess of 40A, but they are not identical and even with the same unit the current requirement varies with temperature and with how long the compressor has been off. This isn't the first report that a 3KW generator failed to be able to start one. 

A typical residential circuit breaker is designed to hold at least 7x its rated current for a few tenths of a second, which is plenty long enough. Depending on its design and protection electronics a generator might or might not be able to do the same thing. Generators store energy in their rotating mass to handle surges, but inverter generators have to be able to pass that power through their electronics without damage. Briggs is limiting those currents more that Honda is, proportional to the continuous power ratings of its generators. That is not a coincidence, I would bet Honda uses relatively higher capacity components than Briggs does. That would increase their costs but provide a higher level of reliability, and that's what we see: Hondas cost more but have a top notch reliability record.  

The Easystart reduces that 40-ish A startup surge by about 2.5-3X, well within the range of a Honda 2K. 

Originally posted by offgrid Some 3kw generators can start the a/c, some can't. Even if you could return the generator, consider the extra size, weight, and fuel use of a larger one. The Easystart is not at all difficult to self-install, and once done its done. Big gennies are backbreakers to load and unload and move around the campsite every time, and depending on your TV can push you over the edge of safety in loading your rig. Other than starting the a/c, there's really nothing you need a big 4.5 kw generator for in an rpod. That's why I opted for a 2kw and the Easystart, the 2kw only weighs about 48 lbs, and converted to propane there is no need for an extra fuel source either.

I can understand a 2K generator not being able to start the AC. I can't see any situation in which a 3K generator would not be able to start and run the AC unless either something is defective in the generator or the AC. If the AC starts without difficulty when powered by shore power, it should start with a 3K generator. After all, it is running on a 15A circuit breaker. That generator should be putting out around 24A steady and 27A surge, which should be more than enough.

A typical 2kw generator would be putting out 1600W steady (14.5A) and 3000W surge (18A). This is a 3kw generator in question. I still think something is wrong with the generator. That is why I suggested contacting the manufacturer for warranty service if it is too late to return it.

Remember too that a 3000 watt generator is 3000 peak (surge) watts, not 3000 running watts. It is rated for 2600 running watts. That generator should be more than capable of starting and running the AC. I have a Generac iX2000 (2200 peak, 2000 running watts) which can start the AC. I did install a Micro-Air EasyStart also and I do recommend it. However, if that generator won't start the AC, I think it indicates a problem with the generator. I would contact the manufacturer and put in a warranty claim since it is not performing as it should.

A clamp-on meter like the Southwire Digital 600-Volt Test Meter which can test both AC and DC amperage is reasonably priced from Lowe's at a little lower price on Amazon.

An Easystart

is a soft start device that is mounted inside your roof air. It is indeed pricey but it works very well, I have one and it allows my Honda 2K to start the a/c. The hardest thing about installing it is that you are working on the roof of the rPod. You have to reconnect a few wires from the existing start capacitor in the Dometic to the Easystart. Then you run the Easystart through a few starts so it can "learn" and minimize the starting load current. The instructions are pretty good, as is the customer support, and several of us have installed them so you can ask any questions you have on the forum.