Air Leak.

Highly doubtful he can cage a brake if he's figuring on having a compressor under the bunk.

 

Sometimes I have had the trailer valve leak like that. But just push in on it some. and it will stop hissing air. If so the block is leaking at the Yellow and Red valves.
Pete

 

Trailer air lines could be frozen up. This happened to me Wednesday morning. I did a pump down test then recharged the system. Engaged the trailer brake valve a few times and that cleared the line out and was good to go.

 

if you are in the cold, and on flat terrain, dont pull the trailer brake when you go to sleep, just the tractor. This will eliminate some things... discovering in the morning you have an air leak, frozen trailer brakes in the winter.

 

If you are in the cold like up here in Michigan, -9 this morning... Put it this way, every morning I wake up and start the truck this past week, I have air leaks galore and coolant dripping from somewhere... Tighten the hose clamps, and let her warm up, all will normally take care of itself. Normal in most cases.

 

I had the same hissing sound from my red valve yesterday, and an even louder hissing from the rear trailer axle. Had to stop at the TA and get a new air bag put on the rear trailer axle.