Trailer air

It has been an exciting 18 hours. Got to my customer last night and pulled in to park for my break since delivery was this morning. Immediately heard the squeal of a pulley or tensioner. Determined it was the idler pulley or tensioner for my A/C compressor belt. Called a dealership in Atlanta and ordered for pickup after this morning's delivery.

Pulled into the rack, all is good except for the squeal. The customer has you park with your front drive axle on a large hump in order to have a good downward slope to your tanker.

Finished unloading, started the engine and I immediately noticed I had dropped a good bit of air pressure. Alarm came on and for some reason had difficulty building air pressure in the usual amount of time. Finally got aired up and pulled out of the rack. Came to stop at the exit gate and while I was breaking I heard air escaping. Windows were down and at first it sounded like it was coming from outside. There was enough air loss that the dash ABS light came on. My immediate concern was to get to the dealer. Made my way there but everytime I had to break, especially for a traffic light, I lost air pressure and the ABS light came on.

Once at the dealer I got out of the cab and depressed the brake pedal thinking I'd hear the noise outside. I believe it was actually coming from the trailer valve in the cab.

I'm not going to be able to mess with this until I stop for the day. I've never had to tear into either the trailer or tractor brake valves. Any ideas as to what I might expect to find?

 

My bad...
2004 PB 379

I only hear the air release/loss while braking.

 

I'm taking this pic from the cab floor...looking up. The one port which does not have an air line connection, is the one blowing out air when I depress the brake pedal. It's marked, "EXH3".

How can I check a spring in a can? I disconnected both air lines from my trailer, pressed on the brake pedal and I got the same air release from that EXH3 port. I think I can say that the problem is with the truck and NOT the trailer, correct?

 

Set ONLY the trailer brake??