Do you have a multi-tester, so you can check to make sure the park pedestal is providing 120 volts on line 1 (L1) and 120 volts on line 2 (L2) from the 50 amp outlet, as kc8lvy and Batts-toy suggested?
You can go to this site, then click the outlet testing tab on the left to see the electrical values you should be getting for a 14-50R outlet. There is a pic of it there with the values in text beside it.
If no multi-tester, there is a quick way to test if you have two air-conditioner units, as one unit will get power from the L1 side and the other will get power from the L2 side.
If both AC units are working, then you are at least getting power on the both L1 and L2 sides in your RV.
If only one AC unit works, then you most likely got a supply problem somewhere.
P.S. I am assuming your trailer is in fact a true 50 amp RV, since you said you were plugged into a 50 amp outlet................and not a 30 amp RV that you are using an adapter to plug into the 50 amp outlet with. Is this assumption correct?