Having a issue on 2019 freightliner ad9si air dryer keeps purging ,changed all lines (charge line,supply line and signal line)installed ball shut off valve in line with gauge on either side on signal line and when dryer builds to cut off and purges close ball valve and the dryer looses its air in the line ,not always though but alot of times been chasing this problem for weeks,have installed 3 dryers now any help would be appreciated