614 Vario Air Handbrake Fault!!! (popping Like Mad)

[vauxhallmaniac]

Hi all hope there's a merc commercial tech head out there, i have recently purchased a 614 vario recovery vehicle 1998 model. the truck has a normal servo operated hydraulic foot brake the handbrake is air operated via a 24v compressor the problem is once the system has made pressure and the handbrake can be released, as you are driving the blow off valve continually pops as though it is building up too much pressure this can be heard over the sound of the engine almost "machine gun like" the previous owner had just replaced the valve prior to me picking it up it would appear this was not the fault!! on a 120 mile drive it was sporadically popping for the first 50 miles then stopped. if im sitting in traffic and it starts if i apply the handbrake to release some air it stops immediately. it seems the more its used the better it gets!! has anybody got a wiring diagram or a diagram of what all the pressure switches do there are at least 4 pressure switches on various parts of the air system,im thinking dodgy pressure sensor or possible relay sticking but have no technical info on the truck any sensible information greatly appreciated many thanks simon..

 

[Xtractorfan]

Is there a valve on the compressor that stops it from overfilling the air tanks..I think this may be sticking or not operating ..

 

[mercedes614]

i am having a major problem with an identical truck, can you let me know the manufacturer of the compressor itself for the handbrake as mone has no tag on it

many many thanks