RV Repair: generator / A/C compatability problem, btu air conditioner, compatability problem

Question
I have a KZ toy hauler-travel trailer.  It was purchased with a standard Onan 4000 generator and a standard RVP 13,500 BTU air conditioner.  We use it for dog shows so the a/c is terribly important.  When the temperature is warmer than 90 degrees outside, as we turn on the a/c, the generator shuts down along with the a/c.  The procedure we use to turn these two units on together is as follows:  First, we run the generator for at least 2 minutes.  Then we switch on the a/c.  Within 60 seconds, when the compressor kicks on the a/c and the generator both shut down.

Again these are the standard units sold with this trailer.  We did not upgrade or switch one brand for another, we followed the manufacturers recommendation.  

We have tested the a/c and generator when the outside temperature is below 90 degrees and the units work fine.  The trailer has a 50 amp service and the a/c has a 20 amp breaker.

Why is there a problem with their compatability of these two units working together when it is hot out? And more importantly, how do we fix this problem?

Thank you for your time,
Sarah Child

Answer
Sarah, You should not have these problems with what you have. It sounds to me like the compressor is either locked up or for some reason it is drawing way too much for the generator to handle. As the temp rises the need for better power is there for the ac. If you have 100 hours on the generator you need to tune it up. If you have something else on with the ac you need to figure out how much it is drawing. You may want to get a meter and check it at one of the 110 sockets inside while you turn on the ac. It should tell you just what is going on and if you want let me know what you find and we can go from there. I hope this helps, Bill