2001 f350- any info on here about diagnosing the vacuum pump running constant and what it takes to fix and or replace?heater blend door operation ok as is the hubs ok.thanks in advance

 

ok the vac pump is a pretty simple device, i would suggest you unplug the line leaving the pump that goes to the vac reservoir. hold your finger over the end to plug it. feel if its pulling a vacuum or not. if it is and the pump stops check for a vac leak. if it is pulling vacuum and the pump keeps running replace the pump. just make sure you dont have a vac leak which i doubt because the pumps dont put out much for vac. most small leaks i have found the pump cant keep up with and run the a/c 4wd controls.

the pump only has 2-wires, 1-hot when enigne is running, and 1-ground wire. the pump has an internal pressure switch to cut the motor off. it sounds like the switch is bad inside the pump causing a continuous run.