[johnkosir]

On 712 there is a check valve that stops air from the 120 v tank from going to the air dryer. on 712 the air dryer is the air protection valve, air comes from the engine compressor and them gets distributed to primary supply (rear brake tank) secondary supply (front brake tank) astronic supply(?) Leveling supply, accessory supply, air chuck . 712 uses Bendex ADHS air dryer, 712 is a early ZF and still has 12 v compressor