1999 F 350 7.3 Diesel, 6 speed 2 WD.
The selector switch that directs cabin air to the window, face feet etc no longer works.
It suddenly stopped one day.
I am guessing that the vacuum pump is gone.
Here is what I did to check it. Let me know please if I have missed anything.
1. All fuses are good.
2. Connector at the pump is clean, tight and no frayed wires.

I disconnected the pump wiring harness connector, put he ignition to run and then plugged the connector back in. I was expecting to hear the pump run and to sense some vacuum from the hose leading out of the pump.

I got nothing.

Is it new pump time?

Regards,
Eric

 

Hi Eric,
If you checked for power and ground at the pump and it's there, then it's replace the pump time.

 

Hanky,
OK. Thank you!
Is this failure common?

Eric

 

Age and use have a lot to do with life of unit.

 

I am not sure if you have purchased a pump yet but if you have not I would suggest OEM. There are a two different part numbers available depending on vehicle options. If the pump is belt driven you will need part number F6TZ-2A451-AA (#F6TZ2A451AA: Vacuum Pump) and if it is an electric drive pump you will need part number 6C3Z-2A451-A (#6C3Z2A451A: Vacuum Pump).