Secondary Air Tank slow to build

[RByrd]

This has probably already been discussed, but I have a 2013 389 and it is very slow to build up air pressure in the secondary tank. Primary tank builds to 100 psi very quickly then it takes 10+ minutes for the dryer to pop off at 130 ish pounds. Once it builds in secondary tank, it holds fine with no trouble. I do not have any major air leaks. I built up air yesterday and just checked it and still has 50 lbs in each tank. I'm guessing it is some type of pressure protection valve that may be sticking, but wanted to ask and see if any of you had any ideas?