I am referring to the 4138 AC unit for 261 truck motor. Does anyone know which vacuum port is intake and which is exhaust or does it matter? This is the fuel pump with the vacuum pump on the bottom of the fuel pump. When I move the pump lever I cannot tell which one is which. There is one port closer to the motor and one further away.
I know one is supposed to go to manifold and one to wipers. Thanks in advance.
