If I remember right, the cab system runs off the tire circuit and not the brake circuit…. So, it seems that a likely relation between the action of disengaging the parking brake and losing inflation would be the hydro cut-off like Suprman said. I think Suprman might be right that the two air lines into the manifold block might be swapped.No. They stay down when i drive... They are up when i park.
So the control knob needs to stay locked in and the level sensor triggers inflation only when needed?
There seems to be some kind of built in logic to the inflation and venting. On my truck, there is a valve under the hydraulic pump with a linkage to the support "bow". It appears to adjust the inflation based on the weight on the lock.I leave mine locked in and on all the time. The manual says to deflate for offroading though. I think its a simple system im not sure there is a sensor I think they behave almost like a shock absorber.