I have a 50 amp RV running a Multiplus 2 and prior to installing the Multiplus AC units ran fine on the generator. After installing the Multiplus when I start one AC it runs fine but when I start the second AC the Multiplus cuts power out to both of them and gives me a L1 overload warning. I am watching the wattage and the power never gets close to the max capacity.
Some AC units start in a almost a dead short condition so it's peak short duration draw is much higher than registered by the system. This can be affected by how long you are starting them up after previous shut down. Or their general condition otherwise.
If the inverter is struggling there can be many reasons why.
One is battery and cabling to it.
You could have input current limit set low so it is taking the load not passing through.
We would need more information on your setup.
What size are the two AC units, what size is the inverter? Battery bank details and set up. Programming?
Are you using the single 120 MP2 or the 2x120? If the 2x120, then you will need to make a few changes to get the full output of the generator to pass thru the multi. Although the 5500 has 2 outputs with separate breakers, it is not a split phase generator so a 2x120 multi will disregard the second line output from the generator.
You'll want to bond L1/L2 together coming out of the generator to produce a single line of 120V. Here's a good explanation of how to do it, CHECK FIRST to make sure there's no voltage between L1/L2 on your generator (make sure they are in phase). They should be, but just make sure.
https://youtu.be/EFxZcF5BtPQ?si=ibBP8LG9oBE37Kqa&t=708
You should probably use an Polaris connector to make the bond vs the way they do it in this video. Something like this:
https://www.amazon.com/OhLectric-OL-38776-Multi-Cable-Connector/dp/B08J7VNM1L?ref_=ast_sto_dp&
