Could be electrical load..
The A/C also requires a good dose of electrical power to start and run the compressor. If the trailer is plugged into household outlet with other things on it, or long and thin electrical cord, the there won't be enough power to the A/C to run it.. There are stories here of compressor damage caused by using extension cords or 15Amp circuits..
Make sure there is enough power getting to the trailer and A/C...
In Theory, there's no difference between Theory and Practice, but in Practice, there is usually a difference...