There was a TSB on the problem and hope it is helpful.
LACK OF A/C COOLING - CLIMATE CONTROL MODE SELECTION NOT WORKING
TECHNICAL SERVICE BULLETIN
Reference Number(s): 05-14-9, Date of Issue: July 25, 2005
FORD:2005-2006 F-Super Duty
Related Ref Number(s): 05-14-9
LACK OF A/C COOLING - CLIMATE CONTROL MODE SELECTION NOT WORKING ISSUE
Some 2005-2006 F-Super Duty vehicles built between 09/15/2004 and 06/08/2005 may exhibit an A/C lack of cooling due to the vent mode select not operating correctly (if panel airflow is selected in AC, Max AC, or vent, the airflow comes out of the defrost vent). Also, on vehicles equipped with the 6.0L diesel engine, the vacuum pump may run excessively.
Check for vacuum leak or blockage (kinked or pinched) and proper routing. Open the glove box to inspect. Inspect for vacuum lines being trapped behind or wrapped around the panel/floor door actuator rod. If vacuum lines are found wrapped around the rod, inspect the lines for damage (leaking or pinched) and repair or replace as necessary. Route the vacuum lines so they are not wrapped around the actuator rod. If replacement is necessary, refer to the following Service Procedure.
VACUUM HARNESS REPLACEMENT PROCEDURE
1. Remove the climate control assembly. Refer to Workshop Manual Section 412-01.
2. Disconnect the two (2) vacuum harness connections through glove box opening.
3. Disconnect push pin fasteners and remove vacuum harness.
4. Install new vacuum harness and secure with push pins.
5. Connect the two (2) vacuum harness connections through glove box opening.
6. Reinstall the climate control assembly. Refer to Workshop Manual Section 412-01.
7. Close glove box.
Part NumberPart Name
5C3Z-19D699-AAVacuum Hose Assembly (With EATC)
5C3Z-19D699-BAVacuum Hose Assembly (Without EATC)
Sunday, December 5th, 2010 AT 7:00 AM