Heat OK AC OK NO Defrost Fan?
 

2002 Dodge 2500 Diesel - All heater settings work fine and all blower speeds work great... Same with A/C all work fine. Issue is no defrost air in either selector setting on the selector knob. The fan stops when defrost is selected.
Any Ideas? I have read a lot about the HVAC but it doesn't seam to be a door issue.
Could it be a bad computer control module? I'm told that there is no connection between the door moving and the blower working.
Just not sure where to look now? [duhhh]

I haven't heard of this problem before so after looking in the book of lines it shows the "mode selector sw" directly provides a ground for the blower in all positions except off. You need a new mode select sw or could try cleaning the contacts with contact cleaner first.

Thanks I will be getting into the mode select this next week and try cleaning first.

In the manual it says that the switches can't be repaired or replaced individually but I know for sure that is not true, you just can't buy them from the dealer individually.

Checked the switch and it must have warn contacts. After switching it a few times (30) or so it started to work. Think I should replace it for a long term fix.
Thanks

Contacts do get dirty so I would try cleaning them with "contact cleaner" from your local electronics store, spray it into the switch and work it LOTS[laugh] it may require 2 or 3 applications before you get it in there and cleaned.