I too learned the hard way about making sure a trailer is charged. I hooked up to it and it required intransit heat. hooked up the lines and opened the valves. Immediately the level in my radiator started dropping. I had 3 gallons of coolant with me so I poured some in, then some more, then some more. It was pouring right out the valve at the back of the trailer..DOH!!!! No one mentioned that valve... Chalk another one up to "live and learn"