3rd AC failure in 3 years

I keep the fifth wheel in a 40x60 steel building with 3 14 foot doors and a 16 foot top height. There's about 4 feet above the ac. We kept it there beginning in Feb 2014 (That's when we bought the house). Prior to that we kept it at a public storage facility that had a covered roof with open sides. Both places had 50amp service. I have always used the SurgeGuard 50amp protector. It's reading 123V tonight and usually does. I unplugged the RV and put the meter to the surgeGuard and both legs are reading 124V. Paperwork: The Oct 2012 replacement traced the problem to a leak. The March 2014 replacement says it was low on refrigerant. I can't be 100% sure but that what it says.