Can someone please help me with my trailer air brake problem???

Okay so I bought my first trailer for an excavating business which is an 86 eager beaver 20 ton tag along. When I picked it up I didn't air it up then when I got back to my shop I applied air and the brakes would not release. So I put a new relay valve in the trailer and now the parking brakes works fine but when I hit the services brakes the brakes lock but won't release. There's is air pressure on the blue gladhand I have to take it off to release the brakes. I'm wondering if it's on my truck the problem when I push in the red trailer knob and step on the brake pedal a constant air supply comes out. So does anyone know what would cause this? I need my trailer next week to move my machines I'm going broke here. Any help is greatly appreciated!

 

I'm not sure because the truck is new to me too but I do have separate tractor and trailer valves.

 

Well I should say that when I first got it a couple months ago I had to put a new cab on because the cab was shot. I'm wondering if I hooked a hose up wrong. So I guess my first question is with the red knob for the trailer pressed in and my foot on the brake pedal should the air be continuous from the blue gladhand or only supply a set amount of air?

 

M sounds like the valve on my truck may be bad then. I appreciate everyone's h

hmm sounds like my valve on the truck might be bad because I can hear it vent through the chambers on the trailer but nothing from the truck. Hopefully that's my problem. I appreciate everyone's help there's no one else to help me