Air in the lines certainly can be a problem but it wasn't mine. My problem was that the Dexter actuator installed with the disc brakes didn't even turn on until greater than 3 volts. That made for no light or light- medium braking with a sudden application when it did finally turn on. Hydrastar and BrakeRite are popular in the RV world and there may be little difference between them. But when I was researching a replacement actuator, Hydrastar technical could not tell me what their minimum turn on voltage was which spooked me. BrakeRite said their voltage was 1.0 volts and my unit actually starts at .9 volts. With the P3 I get good balanced braking at all speeds, light or heavy.