Haldex PUREst dryer failure - casting defect?

[Ronmar]

Yes the top one under the drivers floor with the switch is where the front red glad-hand and air from the park control combine to feed towards the rear. That switch controls the park and emergency lights in the dash.. the lower two valves tied together are blue service glad-hand input to the pri and sec brake systems.

so I wonder where your park control in the dash gets its air from. on the A0 there is a 2way above those floor bulkhead fittings. Straight ahead of your left shin when seated. Where does your gauge box sense pri and sec air? At any rate the 2way that delivers park air to the dash control wouldnt be the cause of a leak, it would be the output line from that 2way or the lines and park control that you have already gone thru.

 

[GeneralDisorder]

The park/emergency controls are supplied by T fittings that also supply the pressure transducers in the MMDC on the passenger side of the treadle valve where there are pass-through supply side ports on the valve:





There are no 2-way valves that I can find under the dash though.

 

[GeneralDisorder]

It is likely the case that I still have cold-induced leaks somewhere. Just not at the moment with 80 degree weather.

For sure the dryer casting issue was causing a leak-down of the wet tank though. Fixing that is helping to improve the situation. It's obviously not the last leak. But the tanks losing air equally at least somewhat narrows the places it could be losing.

 

[GeneralDisorder]

Since the park/emergency controls are a single unit on the newer trucks and are fed from both primary and secondary supply - perhaps the 2-way function is actually inside the control valve assembly? I just remembered that the older trucks have two separate valves while the newer trucks have a manifold valve assembly - Haldex N4400B:

https://www.haldex.com/en/na/valves/hand-control-valves/haldex-newremanufactured/manifold-dash-style-a/kn20611-0f8c73e0/

*Edit* - this appears to be the case. Looking at a video of replacing the A0 valves with the newer manifold valve assembly I see that the older valves had only a single tank supply line that was obviously the output of the 2-way under the dash - in the video Sean has a T with a loop to join the two supply ports on the new manifold valve together. In the manifold style on my truck both primary and secondary supply lines run all the way to the manifold valve assembly. So the 2-way function must be rolled into the manifold.

The other change that was made is there is now not a vent line for the manifold valve. It just has a sintered bronze diffuser on the vent port of the manifold.

 

[Ronmar]

Ok, now I am tracking. You may be right the 2way function to combine either pri or sec may be in the park/trailer control…

on the A0 its a standalone 2way check right at eye level when you open the drivers door…