4X4 Enabled Causing A/C Redirection to Defroster Vents.

[osconda]

On another posting I saw a mention of this problem, but couldn't find any discusion on it.

For those who aren't familiar with the problem...setting 4X4 mode when A/C is ON, causes the air to be redirected to the defroster vents. Switching back to 2WD sends the air back to the dash vents. I'm sure it's related to the vacuum in some way.

Who has fixed this problem? Perhaps you could point me to a previous post on this subject. Thanks

-Osconda
2003 F350, 6.0L, Lariat, Crewcab, FX4.

[DonnieFoxwell]

I had the same problem. Its definetly the vaccum pump. It is covered under warranty if you still have one. Good luck

Donnie

[GrampyJim]

Possible causes include vacuum pump, front knuckle seals, pulsed vacuum solenoid and/or tubing/hoses to knuckles.

When 4X4 is engaged, a strong (~11 inches) vacuum signal is sent to the front hubs for about 30 seconds or so. When 4X4 is disengaged, a much weaker (~5 or 6 inches) vacuum signal is sent to the front hubs.... this also lasts about 30 seconds or so.

After the 30 second period is up, in either case, vacuum supply to the hubs is turned off.

[timeforadmax]

My 02 with a 7.3 was doing the same thing, a vacuum supply lined had poped off.