Is it possible to run 2 13500 btu A/C units off 1 4000 Onan Microquet??

I believe those units run are rated at 120V and 13.5Amps
so 13.5X120X2= That is 3240 Watts, The problem you may have is start up draw. It is close...

Yes, he's right, the startup draw may be a bit close to the limit.

Maybe someone here with some experience can answer that for you. I don't have a 4000 watt, but I did start a 13.5K, and a 15K A/C, then the microwave, a vacuum cleaner and an air compressor all at the same time from an Onan 5500. No problems with any of them, the voltage stayed remarkably stable.

Hopefully someone with some experience can chime in, otherwise it might be a try it and see thing.

yea, it will all depend on how much the 2 ACs will draw if they come on at EXACTLY the same time. if they come on slightly offset from one another i dont see that as an issue. im running two 15K units on a 7500 gen

Thanks, I will be running the extra 12ga wires from the breaker box to the front vent. At least now I know it wont be a waste of time.

Some of the older MH's had an electronic device that let you run both A/C's with a 4000 watt gen set. It would not let both of them start at the same time. I did a quick search but so far have not found any information.

You should consider a high efficiency unit that draws alot less power for the same size.
It is a little more money but as close to the max as you are I would highly suggest it, in fact it is not a bad idea to replace the other one also with the same and sell the existing one. Even then if the compressors start at the same time the breaker on the genny is certain to trip. The way around that is to put in a load/share device, it prevents that and will even turn off one compressor if someone hits a big load like the micro. I think if you dont do something like this your setup will be unpredictable at best.
I have a control box thing that was the predecessor to the load share devices that I never installed, will have to look and see if it will help ya... if so you are welcome to it on the cheap!

You could possibly set one unit to come on a couple degrees after the other. If you install the digital thermostats it would prob work ok. I love having digital thermostats instead of the cheap sliding type. RV.net has the info on how to install.